Heterogeneous Nucleation and Growth of Barium Sulfate at Organic

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Heterogeneous Nucleation and Growth of Barium Sulfate at Organic-Water Interfaces: Interplay between Surface Hydrophobicity and Ba2+ Adsorption Chong Dai, Andrew G. Stack, Ayumi Koishi, Alejandro Fernandez-Martinez, Sang Soo Lee, and Yandi Hu Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.6b01036 • Publication Date (Web): 10 May 2016 Downloaded from http://pubs.acs.org on May 14, 2016

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Heterogeneous Nucleation and Growth of Barium Sulfate at Organic-Water

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Interfaces: Interplay between Surface Hydrophobicity and Ba2+ Adsorption

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Chong Dai1, Andrew G. Stack2, Ayumi Koishi3, Alejandro Fernandez-Martinez3, 4, Sang Soo Lee5, and Yandi Hu1* 1

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Department of Civil & Environmental Engineering, University of Houston, Houston, TX 77004

Chemical Science Division, Oak Ridge National Laboratory, P.O. Box 2008, MS-6110, Oak Ridge, Tennessee 37831, United States 3

Univ. Grenoble Alpes, ISTerre, 38041 Grenoble, France 4

CNRS, ISTerre, 38041 Grenoble, France

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5 Chemical Sciences and Engineering Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439, United States

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*To Whom Correspondence Should Be Addressed

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E-mail: yhu11@ uh.edu

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Phone: (713)743-4285

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Fax: (713)743-4260

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http://www.cive.uh.edu/faculty/hu

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Submitted: March 2016

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Revised: May 2016

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ACS Paragon Plus Environment

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Abstract

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Barium sulfate (BaSO4) is a common scale-forming mineral in natural and engineered

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systems, yet, the rates and mechanisms of heterogeneous BaSO4 nucleation are not understood.

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To address these, we created idealized interfaces on which to study heterogeneous nucleation

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rates and mechanisms, that also are good models for organic-water interfaces: self-assembled

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thin films terminated with different functional groups (i.e., –COOH, –SH, or mixed –SH &

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COOH) coated on glass slides. BaSO4 precipitation on coatings from barite-supersaturated

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solutions (saturation index, SI = 1.1) was investigated using grazing-incidence small angle X-ray

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scattering. After reaction for 1 hr, little amount of BaSO4 formed on hydrophilic bare and –

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COOH coated glasses; Meanwhile, BaSO4 nucleation were significantly promoted on

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hydrophobic –SH and mixed –SH & COOH coatings. This is because substrate hydrophobicity

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likely affected the interfacial energy and hence thermodynamic favorability of heterogeneous

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nucleation. The heterogeneous BaSO4 nucleation and growth kinetics were found to be affected

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by the amount of Ba2+ adsorption onto the substrate and incipient BaSO4 nuclei. The importance

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of Ba2+ adsorption was further corroborated by the finding that precipitation rate increased under

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[Ba2+]/[SO42-] concentration ratios > 1. These observations suggest that thermodynamic

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favorability for nucleation is governed by substrate-water interfacial energy; while given

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favorable thermodynamics, rate is governed by ion attachment to substrates and incipient nuclei.

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Introduction

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Barium sulfate (BaSO4) precipitation plays a crucial role in many natural environment

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and industrial processes.1-5 In geological reservoirs, BaSO4 can precipitate onto rock surfaces

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that can change the surface properties5, 6 and clog pores.7 During industrial processes, BaSO4 can

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precipitate as unwanted scale on oil equipment and facilities as well as on membranes during

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water treatment.1, 5, 8 In addition, during barite precipitation, it can incorporate toxic elements

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(e.g., Ra, Sr) into its structure, so the solubility of a disordered phase (e.g., (Ra, Ba)SO4) often

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governs transport of the contaminant.9

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BaSO4 precipitation starts with nucleation (i.e., formation of initial BaSO4 nanoparticles),

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and proceeds with the growth of BaSO4 through the attachment of Ba2+ and SO42- ions, or

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perhaps other species, onto BaSO4 particles.10 Homogeneous BaSO4 precipitation from

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supersaturated solution has been studied by monitoring changes in aqueous Ba2+ concentration or

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turbidity, without distinction of the nucleation and growth stages. The growth rates of BaSO4

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single crystals have also been studied by tracking step velocity based on atomic force

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microscopy (AFM) measurements,10-16 or by morphological and chemical structural analysis.17

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Although the homogeneous BaSO4 nucleation and growth has been extensively studied, few

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studies have been conducted to understand heterogeneous BaSO4 nucleation and growth; e.g.,

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Pina and et al. investigated the heterogeneous (Ba, Sr)SO4 nucleation and growth on a barite (001)

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surface.18 However, to the best of our knowledge, the initial stages of heterogeneous BaSO4

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nucleation and growth at organic-water interfaces have not been studied,18-20 leading to an

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inability to predict factors that affect the rates of nucleation and growth. Furthermore, previous

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studies have reported that aqueous [Ba2+]/[SO42-] concentration ratios can affect homogeneous

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BaSO4 crystal growth in solution, where excess Ba2+ concentrations can promote the growth of

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BaSO4 crystals more significantly than the excess SO42-,21, 22 and [Ba2+]/[SO42-] ratio strongly

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affects step velocities of single crystals..22, 23 Computational studies have also supported the

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concept of barium ion attachment as a rate controlling process for barite crystal growth.16,24, 25

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Since these studies have examined growth of barite itself, it is therefore not known how the

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interfacial interaction of barium and sulfate ions with a substrate will affect heterogeneous

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nucleation and subsequent precipitation kinetics of BaSO4.

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Heterogeneous nucleation and growth processes could be affected by the various

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interfacial interactions among the aqueous species, the BaSO4 particles, and the substrate

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surfaces. In addition to inorganic solid phases (e.g., minerals, metal), in many natural and

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engineered aqueous environments, various organics are present forming coatings on minerals,

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membranes, or engineered surfaces. These organic coatings can generate organic-water

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interfaces and affect the interactions among substrates, BaSO4, and aqueous species, and

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therefore can influence heterogeneous BaSO4 nucleation and growth at organic-water

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interfaces.26-29 However, neither the rates nor the mechanisms of heterogeneous BaSO4

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nucleation and growth at organic-water interfaces are well understood.

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The objectives of this study are 2-fold: 1) to quantify heterogeneous BaSO4 nucleation

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and growth at different organic-water interfaces, from solutions with various Ba2+/SO42- ratios;

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and 2) To explore the interfacial interactions among Ba2+ and SO42- ions, substrates, and BaSO4

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precipitates and understand the fundamental interfacial processes controlling heterogeneous

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BaSO4 nucleation and growth. To achieve these objectives, grazing-incidence small angle X-ray

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scattering (GISAXS) experiments were utilized to quantify BaSO4 precipitation on bare and

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organic coated SiO2, and multiple interfacial techniques were used to investigate the

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physicochemical interactions at organic-water interfaces.

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Experimental Section

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Preparation of Self-Assembled Thin Films on Glass

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Glass slides (75 × 25 × 1 mm, Superfrost Plus Micro Slide, VWR international) were cut

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into small pieces (10 × 10 × 1 mm). The composition and cleaning procedure of the glass slides

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can be found in our previous publications.30, 31 (3-Triethoxysilyl)propyl succinic acid (TSA) was

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purchased from Gelest Inc and (3-Mercaptopropyl) trimethoxysilane (MT) was purchased from

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Sigma-Aldrich. To prepare –SH or –COOH terminated self-assembled thin films, the glass

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samples were submerged in a mixed solution with 20 wt% TSA or MT and 80 wt% toluene. To

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prepare the mixed –COOH & –SH terminated self-assembled thin film, glass samples were

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submerged in a mixed solution, with 10 wt% TSA, 10 wt% MT, and 80 wt% toluene. After 24 h,

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the coated substrates were rinsed with acetone, to remove the excess amount of loosely-bonded

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molecules. The bare glass and substrates coated with self-assembled thin films were labeled as

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“SiO2”, “-COOH”, “-SH” and “-SH & COOH”.

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The surface morphology of self-assembled thin films was characterized using atomic

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force microscopy (AFM, Figure S6),32-34 while the roughness, thickness and coverage were

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estimated using X-ray reflectivity (XR, at beamline 33-BM-C, Advanced Photon Source, APS).

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Also, surface densities of carboxyl group on –COOH and mixed –SH & COOH coated substrates

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were measured using Toluidine Blue O method (TBO). Detailed information of these

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measurements can be found in the Supporting Information.

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BaSO4 Precipitation Experiments

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Two sets of barium sulfate (BaSO4) precipitation experiments were conducted. The first

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set of experiments was conducted in solutions containing 0.04 mM BaCl2 and 0.04 mM Na2SO4

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on bare and organic coated glass substrates, with fixed saturation index (SI = log(aBaaSO4/Ksp))

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and [Ba2+]/[SO42-] = 1. The second set of experiments was conducted under varying

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[Ba2+]/[SO42-] ratios (115:1, 10:1, 1:10, and 1:115, Table 1) on –SH coated glass substrates using

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a fixed saturation index. As calculated by Geochemist’s Workbench (GWB, Release 9.0,

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Aqueous Solutions LLC), saturation indices (SI, Table 1, Ksp,barite = 10-9.98) of all solutions with

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respect to BaSO4 were 1.1, and the solutions’ pH values were ~ 5.6. The calculated pH values

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agreed well with measured pH values for all solutions, indicating that the thermodynamic

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database used was appropriate.

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Grazing Incidence Small-Angle X-ray Scattering (GISAXS) Measurements

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For each GISAXS experiment, a freshly prepared substrate was placed in a custom built

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GISAXS cell.35-38 Before each measurement, the substrate surface was aligned to the center of

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the incident X-ray beam. Then, 0.7 mL of each freshly mixed solution (Table 1) was injected

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into the cell and the GISAXS measurements started (due to closing the experimental hutch,

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approximately 2 minutes passed from solution preparation to the initiation of data collection).

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During measurements, a small incident angle (0.10°) was chosen to yield high reflectivity of the

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incident X-rays with the energy of 14 keV,39 and scattering from particles formed on the

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substrates was collected by the 2D detector. Scattering patterns were collected every 2 min for 1

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h after the data collection had begun. Experiments were performed at the Advanced Photon

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Source (APS), Argonne National Laboratory (ANL, Beamline 12 ID-B), Argonne, IL.

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All GISAXS data reduction was conducted with GISAXS-SHOP macro, Igor Pro 6.34

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(WaveMetrics, Inc., Oregon). The first image of each GISAXS experiment was chosen as the

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background, which was subtracted from all later scattering images. Based on the two-

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dimensional (2D) GISAXS images, the barium sulfate particles were polydisperse and there were

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no obvious scattering patterns along vertical directions. For simplicity, the shape of particles was

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approximated to a low-resolution, highly symmetric shape, such as a sphere. Therefore, the 2D

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GISAXS images were converted to one-dimensional (1D) scattering curves, i.e., intensity I

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plotted vs. wave factor q (Å-1), by cropping along the Yoneda wing (dqz = 0.007 Å-1), where the

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X-ray scattering signal is the strongest.40, 41 Finally, particle sizes (in radius) were obtained by

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fitting the scattering curves using a log-normal model of non-interacting spherical particles, with

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the IRENA package.42 Lorentz-corrected intensity curves (i.e., I × q2 vs. q, Figure S5) were

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plotted, and the invariant ( Q = ∫ I ( q ) q 2 dq ) evolution (which is proportional to the total particle

∞

0

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volume of the precipitates) was calculated.43 More detailed information about GISAXS data

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analysis can be found in our previous publications.30, 31

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Water Contact Angle Measurements

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Water contact angle (WCA) measurements were conducted using Dataphysics OCA

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15EC for bare and organic coated glass substrates. The substrates were placed horizontally on a

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stage. A drop of distilled water (3 µl) was deposited using a Gastight 500 uL precision syringe

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(Hamilton Co., USA); meanwhile, a video acquisition was obtained using a CCD camera.

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Zeta Potential Measurements

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Two sets of electrophoretic mobility (EM) measurements (Zetasizer Nanoseries, Malvern

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Instruments) were conducted for understanding the interactions among ions, BaSO4 particles,

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and substrates. The first set of EM measurements aimed to measure the zeta potential of BaSO4

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particles in solutions. To generate enough scattering intensity, solutions (Table 1) were prepared

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and concentrated ~100 times by centrifuging using centrifugal filters (Millipore). The

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concentrated solutions were then injected into a capillary cell (DTS1070 folded capillary cell,

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Malvern Instruments) where zeta potentials (ζ) of BaSO4 particles were measured. 7


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In the second set, we aimed to measure zeta potential of bare and organic coated glass

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samples. Cleaned glasses were cut into rectangular pieces (4 mm × 7 mm), adhered to a holder,

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and then coated with organics as described earlier. After coating, the sample holder was placed

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in the surface zeta potential cell (ZEN1020, Malvern Instruments) between two electrodes, and a

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coarse height adjustment was done by an alignment tool. Then, the zeta potential cell was

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inserted into the standard cuvette, and 1.2 mL tracer solution of graphene oxide (GO)

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nanoparticles (pH = 5.7 ± 0.1) was injected into the cuvette. During surface zeta potential

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measurements, the apparent electrophoretic mobility of the GO tracer particles was measured at

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125, 250, 500, 750, and 3000 µm from the substrate surface, and the zeta potentials of the

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substrates were calculated. Triplicate measurements were conducted with good reproducibility.

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More information on surface zeta potential measurement and calculations can be found in

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Supporting Information.

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Ba2+ and SO42- Ion Adsorption

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Ba2+ and SO42- ion adsorption was investigated using dynamic light scattering (DLS),

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quartz crystal microbalance with dissipation (QCM-D, Q-sense E1, Biolin Scientific), and

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attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). Surface zeta

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potentials of bare or organic coated glass samples were measured in the presence of 0.04 mM

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BaCl2 or Na2SO4 at pH =5.7 ± 0.1. The differences in surface zeta potentials of substrates in the

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presence and absence of 0.04 mM BaCl2 or Na2SO4 were evaluated to indicate Ba2+ or SO42- ion

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adsorption.

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Sensors coated with SiO2 (QSX 303, Q-Sense) were purchased from Biolin Scientific,

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and were coated with self-assembled thin films following the same procedures of coating self-

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assembled thin films on glass substrates. Then the sensors were placed into the QCM-D flow 8


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module, and mounted on the Q-sense chamber platform. For initial stabilization, ultrapure water

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was pumped through the flow module at 0.2 mL/min. Then, the testing solution with 0.1 mM

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BaCl2 or Na2SO4 at pH =5.7 ± 0.1 was pumped into the flow module at a constant flow rate of

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0.2 mL/min. The arrows in the Figures of QCM-D measurements indicate switch points from

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ultrapure water to the testing solutions (Figure 4, Figure S3 and S4 in Supporting Information).

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Changes in resonance frequency (∆f) and energy dissipation (∆D) of the sensors were measured,

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which indicated mass changes on the sensors caused by ion adsorption. More details of QCM-D

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measurements can be found in Supporting Information and our previous publication.30

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Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy was

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also used to detect Ba2+ or SO42- adsorption on self-assembled thin films by looking at changes in

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their vibrational frequencies. Self-assembled thin film -coated glasses were exposed to 0.1 M

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BaCl2 or Na2SO4 solutions for 2 hrs with solutions’ pH values adjusted to 5.7 ± 0.1. Then, ATR-

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FTIR measurements were performed using a Nicolet iS 10 (Thermo Scientific) instrument

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equipped with a single-reflection diamond crystal.

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Results and Discussion

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Heterogeneous BaSO4 Precipitation on Bare and Coated Glasses Measured by GISAXS

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GISAXS scattering intensities from BaSO4 particles on different substrates are plotted

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against scattering vector (q, Å-1) (Figure 1) with time-dependent changes resulting from the

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formation of BaSO4 at the surfaces. Almost no change was observed on bare and –COOH coated

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SiO2 surfaces, indicating a low density of BaSO4 particles. Contrarily, the scattering intensity on

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–SH and the mixed –SH & COOH coatings continuously increased throughout the 60 min

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experiments, indicating continuous BaSO4 precipitation at these two coated surfaces. The

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GISAXS observations suggested the promoted heterogeneous BaSO4 precipitation on –SH and

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the mixed –SH & COOH coatings.

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Also, there is a notable difference in the time-dependent changes between these two

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systems. For –SH coated surfaces, significant enhancements to the scattering intensity were

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observed mostly in the lower q region, indicating increases in particle size. In contrast, for the

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mixed –SH & COOH coated substrates, the enhancements were almost proportional over the

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entire q range, indicating increase in number of particles without significant change in size.

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Particle size evolutions throughout the 60 min experiments were obtained from model fitting.

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The average radii of BaSO4 particles on –SH coated substrate grew from 1.3 ± 0.2 to 8.1 ± 0.6

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nm over the course of 60 min; On the other hand, the BaSO4 particles on mixed –SH & COOH

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coated substrate grew slowly from 1.4 ± 0.2 to 3.3 ± 0.4 nm in the same amount of time (Figure

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2A). The evolution of total particle volumes throughout the 60 min reactions are shown in Figure

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2B. Interestingly, the smaller BaSO4 precipitates on the mixed –SH & COOH coating had larger

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total particle volumes compared with those on –SH coating (Figure 2B), indicating a larger

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number of particles on the mixed –SH & COOH coating. As nucleation will increase the number

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of particles and growth will increase particle size, we concluded that heterogeneous BaSO4

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nucleation was faster on the mixed –SH & COOH coatings, while growth was faster on –SH

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coating.

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To understand the favored heterogeneous BaSO4 precipitation on –SH and the mixed –

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SH & COOH coatings than the bare and –COOH coated glasses, also to understand the different

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nucleation and growth rates of BaSO4 on –SH and the mixed –SH & COOH coatings, varied

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interfacial techniques were employed to understand the physicochemical interactions at the

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organic-water interfaces. The mechanisms controlling heterogeneous BaSO4 nucleation and

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growth are discussed from both thermodynamic and kinetic points of view in the following

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subsections.

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Substrate Hydrophobicity Controls Thermodynamic Favorability of Heterogeneous BaSO4

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Nucleation

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Nucleation is the first step during mineral precipitation, and according to classical

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nucleation theory (CNT), at constant supersaturation, differences in free energy barriers for

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heterogeneous nucleation result from changes in interfacial energy (∆Ginterface), as ∆ = + − (1)

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where Alp and Asp are the surface areas of the precipitate–liquid and precipitate–substrate

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interfaces; σlp, σsp, and σls are the interfacial energies of precipitates–liquid, precipitate–substrate,

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and liquid–substrate. For the BaSO4-water interface, free energies of σlp = 135-137 mJ/m2 have

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been observed,44, 45 although much lower values of 20-25 mJ/m2 have also been reported for

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individual surfaces.46,

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substrates. The term σsp is related with the structural mismatch between the substrate and the

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BaSO4 particles, but this is not known for BaSO4-organic interfaces. The term σls has been

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reported to correlate well with the hydrophobicity of substrates.48 Based on water contact angle

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measurements, the hydrophobicity of substrates followed the order: -SH & COOH (89.5 ± 0.6°) >

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-SH (66.4 ± 0.4°) > -COOH (26.4 ± 3.6°) > SiO2 surface (8.3 ± 0.5°) (Figure S1), indicating that

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the values of σls followed the order: -SH & COOH > -SH > -COOH > SiO2 surface. Based on

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eqn. (1), a higher σls correlates with a lower interfacial energy for heterogeneous nucleation. The

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high σls for –SH and mixed –SH&COOH coatings resulted in the lower nucleation free energy

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barriers, which therefore promoted heterogeneous BaSO4 nucleation on the coatings (Figure 1C

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and 1D). On the other hand, the low σls for bare and –COOH coated substrates inhibited

47

Nevertheless, the σlp value will be independent of the presence of

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heterogeneous BaSO4 precipitation on them. The water contact angle and GISAXS

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measurements (Figure 1) suggested that substrate hydrophobicity, σls, was a key parameter

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controlling the thermodynamic favorability of heterogeneous BaSO4 nucleation. This conclusion

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is also in agreement with our previous study on ferrihydrite nucleation, which was also found to

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be controlled by substrate hydrophobicity.35

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It is speculated that the hydrophobicity of the self-assembled thin films can be attributed

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to both molecular and structural properties of the systems. We first considered the difference in

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charged state between the two functional groups (–SH and –COOH). The pKa values of –SH and

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–COOH groups were reported to be in the ranges of 8.4–10.3 and 4.2–4.8, respectively.49-53

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Accordingly, under our experimental condition (pH = 5.7 ± 0.1), less than 1% -SH groups were

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deprotonated to –S-, resulting in the high hydrophobicity of the –SH coating. Meanwhile, more

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than 99 % -COOH were deprotonated to –COO-, resulting in the low hydrophobicity of the –

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COOH coating. Hydrophobicity can also be controlled by surface morphology. However, our

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TBO, AFM, and XR measurements (Figure S6, S8, and Table S1) showed that all the self-

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assembled thin films had similar surface coverage, thickness, and roughness, suggesting that they

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were not the main factors that led to the large hydrophobicity differences among the substrates.

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Therefore, the differences in substrate hydrophobicity were mainly due to the differences in

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terminal functional groups of the organic films. Details of TBO, AFM, and XR measurements

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and results can be found in Supporting Information.

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In summary, from a thermodynamic point of view, substrate hydrophobicity determines if

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heterogeneous BaSO4 nucleation on substrates is favorable or not. Therefore, heterogeneous

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nucleation occurred only on highly hydrophobic surfaces (i.e., -SH and –SH & COOH coatings),

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which likely lowered the interfacial energy. Contrarily, the low hydrophobicity of –COOH

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terminated substrate resulted in high interfacial energy, thus making heterogeneous BaSO4

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nucleation unfavorable.

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Amount of Ba2+ Adsorption onto Substrates Affected Heterogeneous BaSO4 Nucleation and

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Growth Rates

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The favored heterogeneous BaSO4 precipitation on –SH and the mixed –SH & COOH

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coatings was explained from thermodynamic point of view in the above subsection. In this

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subsection, mechanisms controlling the different nucleation and growth rates of BaSO4 on –SH

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and the mixed –SH & COOH coatings was explored from kinetic point of view. Just as growth of

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existing barite crystals is enacted by Ba2+ and SO42- adsorption onto reactive sites,10, 24, 25 so

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heterogeneous barite nucleation on the organic coatings might be enhanced by Ba2+ and SO42-

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ions adsorption at the interfaces. In stagnant aqueous environments, like batch reactors with

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fixed amounts of Ba2+ and SO42- ions, the ion adsorption onto substrates may compete with ion

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adsorption onto pre-existing barite crystals, and thus can affect the rates of heterogeneous BaSO4

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nucleation and growth. The relationship between nucleation density and/or rate and ion sorption

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onto the substrates was investigated using three interfacial techniques: QCM-D, ATR-FTIR, and

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surface zeta potential measurements. QCM-D provides quantitative measurements of the mass of

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ions interacting with a surface; ATR-FTIR provides confirmation of inner-sphere adsorption; and

291

surface zeta potential measurements show how surface charge densities are affected by ion

292

sorption.

293

QCM-D measurements performed under a flowing Na2SO4 solution show that no

294

observable SO42- adsorption onto any substrates occurred (Figure S4 in Supporting Information).

295

In contrast, while no Ba2+ adsorption was observed onto bare SiO2, significant amounts of Ba2+

13


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Page 14 of 32

296

ion adsorbed onto –COOH, -SH, and mixed –SH & COOH coated sensors, with values of 23.5 ±

297

2.9, 6.2 ± 1.5, and 30.6 ± 8.8 ng/cm2, respectively (Figure 4).

298

ATR-FTIR experiments (Figure 5 and S7) also showed no changes in the spectra from

299

the substrates exposed to Na2SO4 solution (Figure S7), whereas new vibrational modes appeared

300

in the range of 2980-3020 cm-1 for the –COOH and mixed –SH&COOH coatings exposed to

301

BaCl2 solutions (Figure 5), indicating that Ba2+ adsorption occurred in an inner-sphere state

302

bound to these two self-assembled thin films (Figure 5). On the contrary, no interaction was

303

observed for Ba2+ with bare SiO2 substrate, and only slight interaction was observed for Ba2+

304

with –SH coating.

305

Zeta potentials of substrates before (ζ) and after (ζ-Ba2+) exposed to BaCl2 solution are

306

summarized in Table 2. Zeta potentials of bare and –SH coated SiO2 in the presence of 0.04 mM

307

Ba2+ (-67.8 ± 1.7 mV and -87.9 ± 8.6 mV, respectively) were similar to those measured without

308

Ba2+ (-64.6 ± 2.6 mV and -82.3 ± 12.5 mV, respectively), indicating the number of charged sites

309

was not significantly affected by Ba2+ adsorption. For –COOH and –SH & COOH coated SiO2,

310

the surface zeta potentials in the presence of 0.04 mM Ba2+ were less negative (-60.3 ± 0.35 and -

311

67.2 ± 6.9 mV, respectively) than in the absence of Ba2+ (-72.6 ± 4.7 and -84.3 ± 6.0 mV,

312

respectively), indicating a significant amount of surface sites were occupied by adsorbed Ba2+.

313

In summary, great consistency was achieved among multiple interfacial techniques: no

314

SO42- adsorption was observed onto any substrate, and the amount of Ba2+ adsorption onto

315

substrates followed the order: on mixed –SH & COOH > –COOH > –SH. The mechanisms

316

controlling Ba2+ adsorption on self-assembled thin films were considered. Previous studies have

317

shown that divalent ions (Ca2+ and Mg2+) can adsorb onto deprotonated –COO- forming –

318

COOCa+ and –COOMg+ species.54, 55 Considering the pKa values of –SH and –COOH groups,4914


Page 15 of 32

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319

53

320

-COOH were deprotonated to –COO-. Therefore, significant amounts of Ba2+ adsorption onto –

321

COOH and mixed –SH &COOH coatings occurred. Furthermore, based on TBO method, surface

322

densities of carboxyl groups on –COOH (i.e., 1.6 ± 0.6 µg/cm2) and mixed –COOH & SH (i.e.,

323

1.3 ± 0.8 µg/cm2) coated substrates were similar, indicating similar amounts of –COOH coatings

324

on both substrates. Therefore, the amount of Ba2+ adsorption onto mixed –SH & COOH coatings

325

was higher than on –COOH coating. The mechanisms controlling the surface coverages of –SH

326

or –COOH on substrates from a mixed –SH & COOH precursor solution were not clear, which is

327

an important direction under our further investigation for future publications.

328

under our experimental condition, less than 0.01% -SH were deprotonated to –S-, while > 99 %

Previous studies reported that Ba2+ dehydration and adsorption, instead of SO42-, onto

329

BaSO4 particles, controls the growth of BaSO4 in solution.11,

330

nucleation and growth studied here, the mixed –SH & COOH coatings can adsorb significant

331

amount of Ba2+. The adsorbed Ba2+ may have acted as nucleation centers and promoted

332

heterogeneous BaSO4 nucleation on the mixed –SH & COOH. As our experiments were

333

conducted in a stagnant system with limited amount of Ba2+, Ba2+ adsorption onto the mixed –

334

SH & COOH coatings resulted in less available Ba2+ to attach to incipient BaSO4 particles, thus

335

slowed down BaSO4 growth. For the –SH coating, there was only a small amount of Ba2+

336

adsorbed, thus perhaps creating fewer nuclei on the coating, which resulted in faster

337

heterogeneous BaSO4 growth. Note that the -COOH coating had a significant amount of Ba2+

338

adsorbed, but did not display substantial nucleation measured by GISAXS. This finding is

339

interesting because it suggests that extensive ion adsorption onto the substrate alone cannot drive

340

nucleation, it must coincide with a thermodynamically favorable substrate-nucleus interaction.

341

Ba2+ Adsorption onto BaSO4: Effects of Aqueous Ba2+/SO42- Ratio on BaSO4 Growth

15


56-58

For heterogeneous BaSO4

Langmuir

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Page 16 of 32

342

To confirm the effects of differences in barium and sulfate ion adsorption on

343

heterogeneous BaSO4 precipitation, BaSO4 precipitation (SI = 1.1) on –SH was quantified under

344

various aqueous [Ba2+]/[SO42-] ratios (115:1, 10:1, 1:1, 1:10, and 1:115).

345

[Ba2+]/[SO42-] = 1 (where particles grew from 1.3 to 8.1 nm within 60 min), with [Ba2+]/[SO42-] >

346

1, faster growth of BaSO4 particles was observed (Figure 2 and 3). As the reaction went on, the

347

increases in both particle size and particle volume occurred more rapidly (Figure 2). Adversely,

348

with [Ba2+]/[SO42-] < 1, the precipitation of BaSO4 particles on –SH coated substrates were

349

slower than [Ba2+]/[SO42-] = 1, with slower increases in both particle sizes and particle volumes

350

(Figure 2 and 3). Dehydration and attachment of Ba2+ has been shown to be a rate limiting step

351

for single crystal BaSO4 growth.24 The observation of heterogeneous precipitation of BaSO4

352

particles on the –SH coating was enhanced with excess amount of Ba2+, is consistent with barium

353

ion attachment also being rate limiting during heterogeneous nucleation and/or initial stages of

354

growth.

355

Summary and Conclusions

Compared with

356

Existing barite growth models do not reflect the initial stages of nanoparticle nucleation

357

and growth processes, especially at organic-water interfaces, but instead tend to focus on the

358

homogeneous growth of existing crystals in solution. In this study, using GISAXS, the kinetics

359

of heterogeneous BaSO4 nucleation and growth at organic-water interfaces under varied aqueous

360

[Ba2+]/[SO42-] ratios were quantified for the first time.

361

Multiple interfacial characterization techniques were employed to probe the interfacial

362

interactions among aqueous ions, the barite particles and the substrates, and the controlling

363

mechanisms of heterogeneous BaSO4 precipitation were systematically explored. Heterogeneous

364

BaSO4 nucleation was found to correlate first with substrate hydrophobicity, which likely affects

16


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Langmuir

365

the favorability of heterogeneous nucleation. Given a sufficiently hydrophobic substrate, inner-

366

sphere Ba2+ adsorption, confirmed by three interfacial techniques, was found to strongly affect

367

both heterogeneous BaSO4 nucleation and subsequent particle growth. Ba2+ adsorption onto the

368

substrates seemingly creates a higher density of nucleation sites; while Ba2+ dehydration and

369

adsorption onto BaSO4 particles has been previously shown to control BaSO4 growth rates.

370

Based on our findings, one can envision a process-based augmentation of classical nucleation

371

theory where the thermodynamic favorability for nuclei formation (based on interfacial energies)

372

determines if nucleation can proceed, but given a favorable interaction, nucleation rates are

373

governed by adsorption of mineral’s constituent ions onto a substrate (i.e., determines nucleation

374

density), and subsequent growth is driven by the attachment and detachment of ions from

375

solution onto the incipient nuclei.

376

Acknowledgements

377

This material is primarily based upon work supported by the U.S. Department of Energy,

378

Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and

379

Biosciences Division, and support C. Dai, A.G. Stack, S.S. Lee, and Y. Hu. A. Koishi and A.

380

Fernandez-Martinez acknowledge funding from the EC2CO (CNRS-INSU) NUCLEATION

381

program, Labex OSUG@2020 (Investissements d’avenir – ANR10 LABX56), and the PICS

382

(CNRS) No. 06736. This project has been funded in part with funds from the State of Texas as

383

part of the program of the Texas Hazardous Waste Research Center. The contents do not

384

necessarily reflect the views and policies of the sponsor nor does the mention of trade names or

385

commercial products constitute endorsement or recommendation for use. We thank Dr. Xiaobing

386

Zuo and Dr. Byeongdu Lee for valuable discussion on GISAXS experiments and data analysis at

387

beamline 12ID-B. Use of the facilities at beamlines Sector 12-ID-B and 33-BM-C at APS was

17


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

388

supported by the US Department of Energy, Office of Science, Office of Basic Energy Science,

389

under Contract No. DE-AC02-06CH11357.

390

Supporting Information:

391

Experimental operation and data analysis details, water contact angle measurements of

392

substrates (Figure S1), GISAXS scattering intensities and Lorentz corrected intensities (Figure

393

S2 and S5), QCM-D measurements with NaCl and Na2SO4 solutions (Figure S3 and S4), AFM

394

(Figure S6), ATR-FTIR (Figure S7), and X-ray reflectivity measurements (Figure S8 and Table

395

S1) of substrates. This material is available free of charge via the Internet at http://pubs.acs.org.

18


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396

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397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439

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19. Pina, C.; Putnis, A.; Astilleros, J. The growth mechanisms of solid solutions crystallising from aqueous solutions. Chem. Geol. 2004, 204, 145-161. 20. Pina, C.; Putnis, A. The kinetics of nucleation of solid solutions from aqueous solutions: a new model for calculating non-equilibrium distribution coefficients. Geochim. Cosmochim. Acta 2002, 66, 185-192. 21. Kucher, M.; Babic, D.; Kind, M. Precipitation of barium sulfate: Experimental investigation about the influence of supersaturation and free lattice ion ratio on particle formation. Chem. Eng. Process. 2006, 45, 900-907. 22. Kowacz, M.; Putnis, C. V.; Putnis, A. The effect of cation:anion ratio in solution on the mechanism of barite growth at constant supersaturation: Role of the desolvation process on the growth kinetics. Geochim. Cosmochim. Acta 2007, 71, 5168-5179. 23. Bracco, J. N. Growth of Sparingly-Soluble AB-type Minerals as a Function of their A: B Ratio. Wright State University2015. 24. Stack, A. G.; Raiteri, P.; Gale, J. D. Accurate rates of the complex mechanisms for growth and dissolution of minerals using a combination of rare-event theories. J. Am. Chem. Soc. 2012, 134, 11-14. 25. Piana, S.; Jones, F.; Gale, J. D. Assisted desolvation as a key kinetic step for crystal growth. J. Am. Chem. Soc. 2006, 128, 13568-13574. 26. Mann, S.; Archibald, D. D.; Didymus, J. M.; Douglas, T.; Heywood, B. R.; Meldrum, F. C.; Reeves, N. J. Crystallization at Inorganic-organic Interfaces: Biominerals and Biomimetic Synthesis. Science 1993, 261, 1286-1292. 27. Rieke, P. C.; Marsh, B. D.; Wood, L. L.; Tarasevich, B. J.; Liu, J.; Song, L.; Fryxell, G. E. Aqueous solution deposition kinetics of iron oxyhydroxide on sulfonic acid terminated selfassembled monolayers. Langmuir 1995, 11, 318-326. 28. Heywood, B. R.; Mann, S. Template-directed inorganic crystallization: oriented nucleation of barium sulfate under Langmuir monolayers of an aliphatic long chain phosphonate. Langmuir 1992, 8, 1492-1498. 29. Zhao, X.; Yang, J.; McCormick, L. D.; Fendler, J. Epitaxial formation of lead sulfide crystals under arachidic acid monolayers. J. Phys. Chem. 1992, 96, 9933-9939. 30. Dai, C.; Hu, Y. Fe(III) Hydroxide Nucleation and Growth on Quartz in the Presence of Cu(II), Pb(II), and Cr(III): Metal Hydrolysis and Adsorption. Environ. Sci. Technol. 2015, 49, 292-300. 31. Dai, C.; Zuo, X.; Cao, B.; Hu, Y. Homogeneous and Heterogeneous (Fex, Cr1-x)(OH)3 Precipitation: Implications for Cr Sequestration. Environ. Sci. Technol. 2016, 50, 1741-1749. 32. Uchida, E.; Uyama, Y.; Ikada, Y. Sorption of low-molecular-weight anions into thin polycation layers grafted onto a film. Langmuir 1993, 9, 1121-1124. 33. Chua, K.-N.; Lim, W.-S.; Zhang, P.; Lu, H.; Wen, J.; Ramakrishna, S.; Leong, K. W.; Mao, H.-Q. Stable immobilization of rat hepatocyte spheroids on galactosylated nanofiber scaffold. Biomaterials 2005, 26, 2537-2547. 34. Ray, J. R.; Lee, B.; Baltrusaitis, J.; Jun, Y.-S. Formation of iron (III)(hydr) oxides on polyaspartate-and alginate-coated substrates: effects of coating hydrophilicity and functional group. Environ. Sci. Technol. 2012, 46, 13167-13175. 35. Hu, Y.; Neil, C.; Lee, B.; Jun, Y.-S. Control of heterogeneous Fe (III)(hydr) oxide nucleation and growth by interfacial energies and local saturations. Environ. Sci. Technol. 2013, 47, 9198-9206.

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36. Hu, Y.; Lee, B.; Bell, C.; Jun, Y.-S. Environmentally abundant anions influence the nucleation, growth, ostwald ripening, and aggregation of hydrous Fe (III) oxides. Langmuir 2012, 28, 7737-7746. 37. Jun, Y.-S.; Lee, B.; Waychunas, G. A. In situ observations of nanoparticle early development kinetics at mineral− water interfaces. Environ. Sci. Technol. 2010, 44, 8182-8189. 38. Hu, Y.; Li, Q.; Lee, B.; Jun, Y.-S. Aluminum affects heterogeneous Fe (III)(Hydr) oxide nucleation, growth, and Ostwald ripening. Environ. Sci. Technol. 2013, 48, 299-306. 39. Henke, B. L.; Gullikson, E. M.; Davis, J. C. X-ray interactions: photoabsorption, scattering, transmission, and reflection at E= 50-30,000 eV, Z= 1-92. Atomic data and nuclear data tables 1993, 54, 181-342. 40. Lee, B.; Seifert, S.; Riley, S. J.; Tikhonov, G.; Tomczyk, N. A.; Vajda, S.; Winans, R. E. Anomalous grazing incidence small-angle x-ray scattering studies of platinum nanoparticles formed by cluster deposition. J. Chem. Phys 2005, 123, 074701. 41. Renaud, G.; Lazzari, R.; Revenant, C.; Barbier, A.; Noblet, M.; Ulrich, O.; Leroy, F.; Jupille, J.; Borensztein, Y.; Henry, C. R. Real-time monitoring of growing nanoparticles. Science 2003, 300, 1416-1419. 42. Ilavsky, J.; Jemian, P. R. Irena: tool suite for modeling and analysis of small-angle scattering. J. Appl. Crystallogr. 2009, 42, 347-353. 43. Li, Y.; Gao, T.; Chu, B. Synchrotron SAXS studies of the phase-separation kinetics in a segmented polyurethane. Macromolecules 1992, 25, 1737-1742. 44. Prieto, M.; Putnis, A.; Fernandez-Diaz, L. Crystallization of solid solutions from aqueous solutions in a porous medium: zoning in (Ba, Sr) SO 4. Geol.Mag. 1993, 130, 289-299. 45. Sangwal, K. On the estimation of surface entropy factor, interfacial tension, dissolution enthalpy and metastable zone-width for substances crystallizing from solution. J. Cryst. Growth 1989, 97, 393-405. 46. Chibowski, E.; Hołysz, L. Influence of tetradecylamine chloride on the surface freeenergy components and flotability of barite. J. Mater. Sci. 1992, 27, 5221-5228. 47. Stack, A. G. Molecular Dynamics Simulations of Solvation and Kink Site Formation at the {001} Barite− Water Interface†. J. Phys. Chem. C 2009, 113, 2104-2110. 48. Dong, J.; Mao, G.; Hill, R. M. Nanoscale aggregate structures of trisiloxane surfactants at solid-liquid interface. Langmuir 2004, 20, 2695-2700. 49. Denison, P.; Jones, F.; Watts, J. X-ray photoelectron spectroscopic analysis of bariumlabelled carbon fibre surfaces. J. Mater. Sci. 1985, 20, 4647-4656. 50. Muto, S.; Ogata, H.; Kamiya, Y. Oxidative addition of organic acids to dioxygen complexes and formation of hydrogen peroxide. Chem. Lett. 1975, 4, 809-812. 51. O'neill, P. Pulse radiolytic study of the interaction of thiols and ascorbate with OH adducts of dGMP and dG: implications for DNA repair processes. Radiat. Res. 1983, 96, 198210. 52. Sober, H. E. Handbook of Biochemistry: The chemial Rubber Co., 1968. 53. Myung, S.; Lee, M.; Kim, G. T.; Ha, J. S.; Hong, S. Large ‐ Scale “ Surface ‐ Programmed Assembly” of Pristine Vanadium Oxide Nanowire‐Based Devices. Adv. Mater. 2005, 17, 2361-2364. 54. Tang, C. Y.; Huang, Z.; Allen, H. C. Binding of Mg2+ and Ca2+ to palmitic acid and deprotonation of the COOH headgroup studied by vibrational sum frequency generation spectroscopy. J. Phys. Chem. B 2010, 114, 17068-17076.

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530 531 532 533 534 535 536 537 538 539 540 541 542

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55. Ito, T. Ion-channel-mimetic sensor for trivalent cations based on self-assembled monolayers of thiol-derivatized 4-acyl-5-pyrazolones on gold. J. Electroanal. Chem. 2001, 495, 87-97. 56. Kucher, M.; Babic, D.; Kind, M. Precipitation of barium sulfate: Experimental investigation about the influence of supersaturation and free lattice ion ratio on particle formation. CHem. Eng. Process 2006, 45, 900-907. 57. Fischer, R. B.; Rhinehammer, R. B. Rapid precipitation of barium sulfate. Anal. Chem. 1953, 25, 1544-1548. 58. Wong, D.; Jaworski, Z.; Nienow, A. Effect of ion excess on particle size and morphology during barium sulphate precipitation: an experimental study. Chem. Eng. Sci. 2001, 56, 727-734. 59. Pulido, T.; Adzerikho, I.; Channick, R. N.; Delcroix, M.; Galiè, N.; Ghofrani, H.-A.; Jansa, P.; Jing, Z.-C.; Le Brun, F.-O.; Mehta, S. Macitentan and morbidity and mortality in pulmonary arterial hypertension. N. Engl. J. Med. 2013, 369, 809-818.

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Table 1. Solution Conditions

544

Aqueous Ba2+/SO42ratio (R) R = 1:1 R = 10:1 R = 115:1 R = 1:10 R = 1:115

BaCl2, mM

Na2SO4, mM

ISa, mM

pHb

SIc

0.040 0.120 0.400 0.012 0.004

0.040 0.012 0.003 0.120 0.460

0.24 0.39 1.20 0.39 1.37

5.61 5.61 5.61 5.62 5.62

1.1 1.1 1.1 1.1 1.1

545

Note: ISa: Ionic Strength. pHb: initial pH values, calculated by GWB, which were consistent with

546

measured pH values. SIc: Saturation indices (SI= Log (Q/Ksp) with respect to barite, which were

547

calculated using GWB.

548

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Table 2. Substrate Properties

549

Water contact ζa, ζ-Ba2+ b, Ba2+ adsorption, angle (°) mV mV ng/cm2 SiO2 8.3 ± 0.5 -64.6 ± 2.6 -67.8 ± 1.7 N/A -COOH coating 26.4 ± 3.6 -72.6 ± 4.7 -60.3 ± 0.35 23.5 ± 2.9 -SH coating 66.4 ± 0.4 -82.3 ± 12.5 -87.9 ± 8.6 6.2 ± 1.5 -SH & COOH coating 89.5 ± 0.6 -84.3 ± 6.0 -67.2 ± 6.9 30.6 ± 8.8 a 2+ 2+ b Note: ζ : The zeta potentials of substrates in the absence of Ba ; ζ-Ba : The zeta potentials of Substrates

550 551

Page 24 of 32

substrates in the presence of 0.04 mM Ba2+.

552 553

554

555

24


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556

List of Figures

557

Figure 1. GISAXS scattering intensities generated by BaSO4 particles formed in the mixed

558

solutions of 0.04 mM BaCl2 and 0.04 mM Na2SO4 (pH = 5.6 ± 0.2) on bare glass SiO2

559

(Figure 1A, SiO2), and self-assembled thin films terminated with -COOH (Figure 1B),

560

-SH (Figure 1C), and mixed -SH & COOH (Figure 1D). The experimental data are

561

shown as colored dots, while the fitted curves are shown as black lines. Particle

562

growth are indicated by the red arrows (Figure 1C and 1D), where the peak positions

563

shift to lower q ranges.

564

Figure 2. Under solution conditions listed in Table 1, radii (Figure 2A) and relative total

565

volumes (Figure 2B) of BaSO4 particles form on -SH and mixed -SH & COOH coated

566

substrates. For data obtained with high aqueous Ba2+/SO42- ratio (R = 10:1 and 115:1),

567

the sizes of BaSO4 particles at later stage are too big and are out of GISAXS

568

measurement range. Therefore, their size and volume cannot be calculated.

569

Figure 3. GISAXS scattering intensities generated by BaSO4 particles formed on –SH coatings

570

from solutions with varying aqueous Ba2+/SO4 ratios (R = 115:1 in panel A; R = 10:1

571

in panel B; R= 1:10 in panel C; R = 1:115 in panel D). The experimental data are

572

shown as colored dots, while the fitted curves are shown as black lines

573

Figure 4. QCM-D measurements with 0.1 mM BaCl2 solution and sensors coated with SiO2

574

(Figure A), and self-assembled thin films terminated with -COOH (Figure B), -SH

575

(Figure C), and mixed -SH & COOH (Figure D). The decreases in frequency (∆f)

576

indicate the adsorption of Ba2+ ions onto sensors.

25


Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 32

577

Figure 5. ATR-FTIR measurements of bare glass and self-assembled thin films on -coated

578

substrates in water and 0.1 mM BaCl2 solution. In the frequency range from 2830-2970

579

cm-1, characteristic vibrational frequencies of symmetric and antisymmetric stretching

580

modes of υ(CH2) are presented.59 The vibrational spectrum of pure SiO2 shows the

581

presence of a residual organic compound, probably due to traces of ethanol adsorbed after

582

cleaning. The spectra of organic-coated substrates are slightly different from that of pure

583

SiO2, with maxima for the stretching modes shifted to higher frequencies than that of the

584

residual organic from SiO2. Compared with spectra measured in water, the spectra for –

585

SH, -COOH, and mixed –SH&COOH coatings measured in 0.1 mM BaCl2 solution show

586

additional peaks in the range of 2980-3020 cm-1, indicating Ba2+ adsorption onto the

587

substrates.

588 589

26


Page 27 of 32

Figure 1.

10 10 10

4 min 8 min 14 min 20 min 30 min 40 min 60 min

4

3

2

1

10

4

10

3

10

2

10

1

5 6

2

3 4 5 6 -1

0.01 q_xy (Å

)

10

0.1

5 6

2

0.01

3

q_xy (Å

4 5 6 -1

)

D. -SH&COOH

C. -SH

B. -COOH

5

10

10 10 10 10

0.1

5

10 Intensity (counts)

10

A. SiO2

5

Intensity (counts)

10

Intensity (counts)

590

Intensity (counts)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

4

3

2

1 5 6

2

0.01

3 4 5 6 -1

q_xy (Å

591 592

27


)

10 10 10 10

0.1

5

4

3

2

1 5 6

2

3

4 5 6

0.01 q_xy (Å-1)

0.1

Langmuir

593

Figure 2.

B. Total particle volume

-SH R=1:1 -SH & COOH R=1:1 -SH R=115:1 -SH R=10:1 -SH R=1:10 -SH R=1:115

12 10 8 6 4 2

Total particle volume (relative unit)

A. Particle size

Radius, nm

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 32

0 0 594

10

20

30

40

50

0.6 0.5 0.4 0.3 0.2 0.1 0.0

60

0

10

20

30

40

Time, min

Time, min

595

28


50

60

Page 29 of 32

Figure 3.

A. -SH (115:1) 10 10 10 10 10

6 5 4 3 2

B. -SH (10:1) 7

10

10

6

10

Intensity (counts)

10

4 min 8 min 14 min 20 min 30 min 40 min 60 min

Intensity (counts)

10

7

5

10

4

10

3

10

2

10

1

1

10 5 6

2

0.01

3

4 5 6 -1

q_xy (Å

)

5 6

0.1

2

0.01

3

q_xy (Å

10 10 10 10 10

4 5 6

0.1

-1

10

)

C. -SH (1:10)

7

D. -SH (1:115) 7

10

6

6

Intensity (counts)

596

Intensity (counts)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

5 4 3 2 1

10

5

10

4

10

3

10

2

10

1

5 6

2

0.01

3

q_xy (Å

597 598

29


4 5 6 -1

)

10

0.1

5 6

2

0.01

3

4 5 6 -1

q_xy (Å

)

0.1

Langmuir

599

Figure 4.

A. Glass

B. -COOH

4 ∆ f (HZ)

∆ f (HZ)

4

0.1 mM BaCl2

2 0

-4

-4

10

20

30

Time, min

0

10 20 Time, min

C. -SH

D. –SH & COOH

∆ f (HZ)

4 2

0.1 mM BaCl2

0

-2 -4 0

0.1 mM BaCl2

0

-2

0

600

2

-2

∆ f (HZ)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 32

10 20 Time, min

30

4 0.1 mM BaCl2 2 0 -2 -4 0 10 20 Time, min

30


30

30

Page 31 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Figure 5.

31


Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 32

TOC

Heterogeneous nucleation

Hydrophobicity

Substrate coatings

BaSO4

Ba2+ and SO42- ions

32


Heterogeneous Nucleation and Growth of Barium Sulfate at Organic

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