How cellulose nanofibrils affect bulk, surface, and foam properties of

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How cellulose nanofibrils affect bulk, surface, and foam properties of anionic surfactant solutions Wenchao Xiang, Natalie Preisig, Annika Ketola, Blaise L. Tardy, Long Bai, Jukka Aukusti Ketoja, Cosima Stubenrauch, and Orlando J. Rojas Biomacromolecules, Just Accepted Manuscript • DOI: 10.1021/acs.biomac.9b01037 • Publication Date (Web): 03 Sep 2019 Downloaded from pubs.acs.org on September 4, 2019

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How cellulose nanofibrils affect bulk, surface, and foam properties of anionic surfactant solutions Wenchao Xiang†, Natalie Preisig§, Annika Ketola,┴ Blaise L. Tardy†, Long Bai†, Jukka A. Ketoja,// Cosima Stubenrauch§,*, Orlando J. Rojas†,*

†Bio-based

Colloids and Materials, Department of Bioproducts and Biosystems, School of

Chemical Engineering, Aalto University, P.O. Box 16300, FI-00076 Aalto, Espoo, Finland §Universität Stuttgart, Institut für Physikalische Chemie, Pfaffenwaldring 55, 70569 Stuttgart,

Germany ┴VTT

Technical Research Centre of Finland Ltd, P.O. Box 1603, FI-40101 Jyväskylä, Finland

//VTT

Technical Research Centre of Finland Ltd., P.O. Box 1000, FI-02044, Espoo, Finland

transportation applications. Understanding behavior media their vital both research applications, industrial to infl many such treatment, reactions, evolution recovery valuable However, behaviors gas mainly by which force, impedes any except Consequently, spontaneous directional aqueous still big hydrophobic superbeen fabricated chemical low-surface-tension integrating morphology. copper superhydrophobic ated genercapable transporting from bubbles base and underwater, when vertically with up. study inspire develop strategies achieve of manipulation practical their gas the The issue. bubbles uences directional other directionally identifi importance spontaneously scientifi conical tips spontaneous as successfully their they will processes, bubbles and greatly buoyant upward. cones people dominated signifi waste of effi present in novel media and gas minerals. pointing of coatings direction fi to Here, and of the by gas tip realizing are aqueous on xed gas ed cient in even gas bubble and owing The care have to water the to cant the in as the are is the in of a ABSTRACT

We study the generation and decay of aqueous foams stabilized by sodium dodecyl sulfate

(SDS) in the presence of unmodified cellulose nanofibrils (CNF). Together with the rheology of aqueous suspension containing CNF and SDS, the colloidal interactions are determined by Quartz Crystal Microgravimetry with dissipation monitoring, Surface Plasmon Resonance, and Isothermal Titration Calorimetry. The results are used to explain the properties of the air/water interface (interfacial activity and dilatational moduli determined from oscillating air bubbles) and of the bulk (steady-state flow, oscillatory shear and capillary thinning). These properties are

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finally correlated to the foamability and to the foam stability. The latter was studied as a function of time by monitoring the foam volume, the liquid fraction, and the bubble size distribution. The shear-thinning effect of CNF is found to facilitate foam formation at SDS concentrations above the critical micelle concentration (𝑐𝑆𝐷𝑆 ≥ cmc). Compared with foams stabilized by pure SDS, the presence of CNF enhances the viscosity and elasticity of the continuous phase as well as of the air/water interface. The CNF-containing foams have higher liquid fractions, larger initial bubble sizes, and better stability. Due to charge-screening effects caused by sodium counterions and depletion attraction caused by SDS micelles, especially at high SDS concentrations, CNF forms aggregates in the plateau borders and nodes of the foam, thus slowing down liquid drainage and bubble growth and improving foam stability. Overall, our findings advance the understanding of the role of CNF in foam generation and stabilization.

Keywords: Foam and surface properties; cellulose nanofibrils; CNF aggregates; elasticity; shear thinning; bubbles; foamability; stability; anionic surfactants

[2] Gas aqueous ubiquitous industrial world, and Examples lizations utibubble treatment, valuable of from pressure [1] while, liquid systems serious blockages, reducing ment as Understanding Meanwasting daily bubbles ores, lifetime transportation gas in erosions could media sensors. minerals of the life. wastewater production, include recovery bubbles and resources. resource in further gas in equipnatural as cause are the and well the in INTRODUCTION

Aqueous foams are important in numerous applications1–3 for which often a precise control of

the foam generation and stability is required.4–8 Typical destabilizing processes are drainage, coalescence, and coarsening,9–13 all of which may occur simultaneously.14 Drainage can be slowed down by increasing the viscosity of the continuous phase; in turn it improves the foam’s resistance against coalescence. In addition, generating monodisperse bubbles or reducing the permeability of


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the foam films leads to a slower bubble growth via coarsening (owing to Laplace pressure gradients).14,15 A large number of surfactants, proteins, and particles has been used to control the generation and stabilization of foams.16–19 Sustainable and renewable materials, such as cellulose nanofibrils (CNF),20 have been used to enhance the properties of foams and are becoming increasingly popular in the application of multiphase systems,6 including emulsions.21 CNF is a biosynthesized supramolecular construct of cellulose chains. -1,4-linked anhydro-D-glucose, as the basic unit of cellulose, provides the CNF surfaces with abundant hydroxyl groups. These hydroxyl groups enable various modifications of CNF, such as hydrophobization for improved air/water interfacial activity.22 So far, CNF-based foam studies have focused on tuning the CNF surface chemistry via physical adsorption or chemical modification into more anionically-charged CNF, i.e., TEMPOCNF.23 However, the exploration of native CNF for foam generation and its associated decay has not been studied yet, although it is of fundamental importance. Furthermore, native CNF mechanically disintegrated from wood fibers, carries residual non-cellulosics (i.e., lignins, hemicelluloses, among others), which have been recently proven to be surface active.24–27 Hence, there is a pressing need to explore native CNF, as a construct of cellulose decorated with surfaceactive non-cellulosics, for applications involving air/water interfaces. In the study at hand, we aim to explore the impact of nanofibrillated wood fibers, i.e., native CNF, on the properties of the bulk and the air/water interface of a surfactant-containing solution. Specifically, due to their large aspect ratio and high flexibility, the presence of CNF in aqueous suspensions promotes shear-thinning28 and thixotropy29 and results in gels at relatively low CNF concentrations.30 Hence, CNF is a promising candidate for slowing down drainage, coalescence and coarsening, especially given its gelling properties at low shear rates.



In this study, different concentrations of sodium dodecyl sulfate (SDS) were used in diluted CNF suspensions (0.3 wt %) to generate wet foams. SDS was chosen since it has minimal interactions with CNF given the fact that both are negatively charged.31 The influence of CNF on SDS foam generation and stabilization was investigated by monitoring (1) the air/water interfacial activity and dilatational (elastic) modulus; (2) the rheological behavior (under extension, steadystate and oscillatory shear) of the bulk systems and their colloid stability (zeta potential and others) and, (3) the foam structure as a function of time (foam volume, liquid fraction, bubble size). The results allow us to elucidate the impact of unmodified CNF on foam generation and stability, responding to the need to further our knowledge in a subject that has remained largely unexplored, especially when considering the associated fundamental aspects.

EXPERIMENTAL Materials. Sodium dodecyl sulfate (SDS) (purity ≥ 99.0%), Calcofluor white stain, and poly(ethylene imine) (PEI, Mw = 50000-100000) were purchased from Sigma-Aldrich and used as received. The cellulose nanofibrils (CNF, 1.67 wt %) were obtained from high-pressure microfluidization (Microfluidics Crop., USA) by passing six times never-dried, bleached birch fibers through a chamber pair (200 m and 100 m) arranged in series, under a pressure of 2000 bar. Milli-Q (MQ) water or double distilled water was used throughout the experiments. Characterization of CNF. The dimensions of the CNF were determined by transmission electron microscopy (TEM, JEOL JEM-3200FSC, operated at 300 kV). The TEM samples were prepared by casting a drop of 0.01 wt % CNF on a plasma-cleaned holey carbon grid. After drying, the images were recorded with a Gatan CCD camera and processed with Gatan Digital Micrograph software.


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The zeta potential and conductivity of CNF (0.3 wt % aqueous suspension) in the absence and presence of SDS (0.7, 8.4, and 70 mM) were measured by a Zetasizer Nano (ZS-90, Malvern Instruments). Triplicate measurements were carried out for each freshly prepared sample. The stability was assessed with an optical microscope (Leica DM 750) after mixing for 30 min. Air/water surface tension. The air/water surface tension (γ) was measured with a tensiometer (Attension Theta, Biolin Scientific, Finland). For this purpose, an air bubble (2.5-4 µL) was injected in the liquid via a hook needle (outer diameter: 0.7176 mm). The measured samples, including MQ water, SDS solutions (0.7-70 mM), and 0.3 wt % CNF suspensions in the absence and presence of SDS (0.7-70 mM), were placed in a quartz cuvette. The air/water interfacial tension γ measured with bubbles equilibrated at room temperature was determined from recorded high-speed digital videos. The equilibration time for MQ water and 0.3 wt % CNF suspensions in the presence and absence of 0.7-7 mM SDS was 20 min. For all the other samples it was 10 min. Duplicate experiments were conducted for each freshly prepared sample. The endpoint of the recorded data was used to calculate the average γ and standard deviation for each sample. Rheological behavior. Air/water dilatational interfacial rheology. The viscoelastic properties of the air/water interface were measured with an optical tensiometer by recording the perturbation of the size of a bubble under oscillation and the air/water interfacial tension (Attension Theta, Biolin Scientific, Finland). The oscillation was achieved with a piezo-pump enclosed in a chamber and driven through a pulse-modulating electronic unit (Pulsating drop module, PD-200). The interfacial tension measurements were conducted during 1 min while the bubble was oscillated at a frequency of 0.5 Hz using a volume amplitude of 0.8 µL. A stable range of oscillation period was used in plotting the surface tension isotherms. The complex dilatational interfacial modulus



(Ed) and its elastic component (Ed′) were calculated using the OneAttension software (Biolin Scientific, Finland), which relied on the recorded videos. Duplicate measurements were performed for each freshly prepared sample, i.e., MQ water, SDS solutions (0.7-70 mM), as well as 0.3 wt % CNF suspensions in the absence and presence of SDS (0.7-70 mM). Rheology under shear/oscillation. The rheological properties of CNF suspensions (0.3 and 1.5 wt %) in the absence and in the presence of SDS (0.7, 8.4, and 70 mM) as well as those of pure SDS solutions (0.7, 8.4, and 70 mM) were characterized with a rheometer (MCR300 Anton Paar) operated with a plate-plate geometry (steel, diameter 25 mm, gap 1 mm). All measurements were conducted at 21.0 ºC. Serrated plates were used to minimize wall slippage. Pre-shearing of the samples was carried out at a shear rate (γ) of 1 1/s, followed by a resting time of 10 min before data acquisition. The apparent viscosity () was measured as a function of γ in the frequency range between 0.01 and 100 1/s. Amplitude sweeps (between 0.01-100 %) were conducted at 1 Hz to measure the storage and loss moduli, G′ and G′′ and to establish a strain amplitude of 0.1% for the successive frequency sweep measurements. The angular frequency () of the oscillatory shear was varied between 0.1-100 rad/s to obtain the corresponding G′ and G′′, as well as the complex viscosity (*). Capillary thinning. The apparent extensional viscosity (𝜂𝐸) of SDS solutions (8.4 and 70 mM) in the absence and presence of 0.3 wt % CNF was measured at room temperature with a Haake capillary breakup extensional rheometer (Thermo Scientific Inc.). The sample was loaded between the flat face of solid cylinders (6 mm a diameter) initially separated by 1.99 mm (initial aspect ratio = 0.66). After a rapid lift of the upper cylinder, the final separation was set at 8.98 mm (final aspect ratio = 2.99). The diameter of the capillary was monitored with a laser beam. Before any measurement, each sample was relaxed for 1 min upon loading. The tests were repeated five times 6 ACS Paragon Plus Environment

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for each sample. The most representative data were selected for further discussion. Assuming an axially symmetric shape of the capillary, the Hencky strain (𝜀𝐻𝑒𝑛𝑐𝑘𝑦) (true extensional strain) during the capillary breakup of the given sample was calculated from equation (1):

𝐷0

(1)

𝜀𝐻𝑒𝑛𝑐𝑘𝑦 = 2ln ( 𝐷 )

where D0 and D are the initial and time-dependent diameters of the thinning capillary, respectively. The extension viscosity (𝜂𝐸) during capillary thinning was determined from equation (2) using the values of the surface tension :32

γ

(2)

𝜂𝐸 = ― 𝑑𝐷/𝑑𝑡

Foam generation and characterization. The SDS-stabilized liquid foams (0.7, 8.4, and 70 mM SDS concentration), in the absence and presence of CNF (0.3 wt %), were studied with a FoamScan unit (Teclis, France) equipped with two CCD cameras and five electrodes placed along a foam column. Firstly, 50 mL of CNF suspension was bath-sonicated for 10 min to disperse the nanofibrils and remove any entrapped bubbles. Thereafter, a certain amount of a stock SDS solution (315 mM concentration) and double distilled water were added to the CNF suspension to get a total volume of 65 mL with 0.3 wt % CNF and the desired SDS concentrations (0.7, 8.4, and 70 mM). Each suspension was gently mixed under magnetic stirring for 1 min before foam generation. The sample volume used for the foam generation experiments was kept constant at 60 mL. The flow rate of nitrogen gas used to generate the foams was set to 84 mL/min. The nitrogen gas was purged into the foam column through a porous glass disc (pore diameters in the range of 41-100 7 ACS Paragon Plus Environment


m). The foam volume (𝑉𝑓𝑜𝑎𝑚) was monitored by recording the foam column images using one of the CCD cameras. The foamability was evaluated by recording the time taken to reach a foam volume of 120 mL. After the gas flow stopped, the foam stability was assessed by recording the foam volume and the liquid fraction over time. The maximum foaming time and the total experimental time were set at 2000 s (~33 min) and 2200 s (~37 min), respectively. Duplicate tests were run for each sample. The liquid fraction (𝜀) in the foam was determined by measuring the conductivity from the second electrode located at a height of 80 mm (~ 23 mm above the initial liquid level). The conductivity of each sample in the foam column was calibrated by using the first electrode located above the porous glass disc. The foam structure was followed by recording images of the foam bubbles using the second CCD camera located at a height of 105 mm (~ 48 mm above the initial liquid level). The bubble images were processed with freeware program ImageJ (version: 1.50i) to construct a water-free skeleton. This was done by reducing the dark areas around the bubble periphery to lines of onepixel width. With the skeletonized images, the number-averaged bubble sizes () and the bubble size distributions (PDI, polydispersity index) were determined with the Cell Size Analysis (CSA) software. The standard deviations of and PDI were calculated based on duplicate experiments and plotted as error bars in the respective profiles. The presence of CNF in SDS foams (8.4 mM) was detected by a polarization microscope (Leica DM 4500, Germany) with an attached fluorescent imaging probe. The CNF was stained with Calcofluor white (exc/em = 365/435 nm) at least 1 min prior to imaging. The images were taken from foams after resting (for at least 3 min) on a concave glass slide.


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RESULTS and DISCUSSION Air/water interfacial properties. The surface tension isotherms for SDS in MQ water (SDSaq) and in 0.3 wt % CNF (SDSaq+CNF) were determined from the changes in an air bubble formed at the tip of a hook needle, Figure 1. The used setup minimizes the effect of any external disturbance, such as perturbations caused by air flow and anisotropic stresses induced by the materials.33 The surface tension isotherm for SDS in the presence of CNF (0.3 wt % CNF, Figure 1, filled symbols) is found to be similar to that of SDS in water (Figure 1, open symbols). The critical micelle concentration of the SDSaq+CNF (cmcmixture) is similar to that of SDSaq (cmc = 8.4 mM, in agreement to reported values34). At concentrations above 3.8 mM SDS, the values of the surface tension of SDSaq+CNF are clearly lower than those of SDSaq, which is ascribed to the surfaceactive compounds that leach from the fibrils, as reported in our previous study.27



Figure 1. Surface tension (γ) isotherms for SDS in MQ water (SDSaq, open symbols) and in the presence of 0.3 wt % CNF (SDSaq+CNF, filled symbols) measured at room temperature. The images in the insets illustrate the air bubble formed at the tip of a hook needle in 0.7 mM SDS in the absence and presence of 0.3 wt % CNF.

Once the equilibrium air/water interfacial tension is reached, the air bubble is oscillated to study the effects of compression and expansion at the air/water interface. Figure 2a indicates that the surface tension of SDS solutions at a submicellar concentration (𝑐𝑆𝐷𝑆 < cmc) follows the sinusoidal volume changes of the bubble. In contrast, at 𝑐𝑆𝐷𝑆 ≥ cmc, the surface tension is fairly independent on the oscillation of the bubble volume (Figure 2b for 𝑐𝑆𝐷𝑆 = cmc and Figure S1b for 𝑐𝑆𝐷𝑆 > cmc). The latter behavior is caused by the fact that the diffusion of SDS to (expansion) and away (compression) from the interface is faster than the oscillation. In the case of the SDSaq+CNF, the surface tension follows the oscillation of the bubble volume at SDS concentrations below and above the cmc (Figure 2c,d and S1c,d). Additionally, compared to the results for the pure SDS solution (Figure 2a,b), the presence of CNF leads to a higher oscillation amplitude (Figure 2c,d), most significantly observed at 𝑐𝑆𝐷𝑆 < cmc. The slower γ recovery during oscillation in the presence of CNF is speculated to be the result of surface-active aggregates formed between the anionic surfactant and non-cellulosic leachates originating from the fibrils. These surface-active aggregates diffuse slower compared to SDS molecules due to their larger hydrodynamic radius.27 The surface activity of the leached materials from CNF is shown by the reduced surface tension of CNF suspensions compared to that of MQ water (Figures S1c and S1a). In the presence of SDS, these aggregates with the non-cellulosic leachates are more surfaceactive27 at 𝑐𝑆𝐷𝑆 ≥ cmc (see also Figure 2b,d and Figure S1b,d). Finally, comparing the complex dilatational interfacial modulus (Ed) and its elastic component (Ed') of the SDSaq+CNF and the


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corresponding SDSaq solutions (Figure 2 and S1), one can conclude that CNF renders the air/water interface more elastic.

Figure 2. The air/water interfacial tension (γ, left y-axis) and bubble volume (right y-axis) as a function of the oscillation time (tosc) for (a) 0.7 mM and (b) 8.4 mM (= cmc) SDS solutions. The corresponding isotherms for SDSaq+CNF (containing 0.3 wt % CNF) are also shown (c and d). The values of the complex dilatational interfacial modulus (Ed) and its elastic component (Ed') of each system are given.

Bulk properties. Rheological behavior. Figure 3a shows the flow curves of pure SDS solutions (0.7, 8.4, and 70 mM) and pure CNF suspensions (0.3 and 1.5 wt %) as well as the corresponding SDSaq+CNF. As expected, the SDS solutions display a Newtonian behavior (the 11 ACS Paragon Plus Environment


apparent viscosity, η, is independent of the shear rate, Figure 3a, open symbols). Note that the transient fluctuation in the SDS viscosity profiles is an artifact given the limits of the rheometer’s geometry, which is not ideal to test fluids of low viscosity. The apparent viscosity and shearthinning behavior of SDSaq+CNF show similar trends to those of pure CNF suspensions. This illustrates the dominating role of the cellulose fibrils, caused by their large size aspect that induces entanglement at relatively low concentrations (Figure 3b). The apparent viscosity of SDSaq+CNF increases with increasing CNF concentration from 0.3 to 1.5 wt % (Figure 3a, gray- to blue-filled symbols).


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Figure 3. (a) Apparent viscosity () of aqueous SDS solutions at 0.7 mM (open triangles), 8.4 mM (open squares) and 70 mM (open diamonds). The apparent viscosity profiles for the 0.3 wt % and 1.5 wt % of CNF suspensions in the absence (gray- and blue-filled circles, respectively) and in the presence of SDS (the same symbol nomenclature as for the pure SDS solutions) at their respective concentrations are shown. (b) Dimensions of the cellulose nanofibrils observed with a TEM microscope. The sample was prepared from 0.01 wt % CNF. At 1.5 wt % CNF the entanglement and percolation of the fibers are typical for a hydrogel (inset picture).

Similar to the shear-thinning behavior under steady-state flow (Figure 3a), the complex viscosity (η*) of SDSaq+CNF monotonically decreases over the whole range of the angular frequency sweep (Figure 4a). However, the η*-values are one order of magnitude higher than the ηvalues at the corresponding shear rates/angular frequencies. This observation is explained by wall-

depletion effects during the steady-state flow measurements, the break of CNF flocs, as well as fibril stretching and alignment under unidirectional shear.35,36 Thus, the η*-values characterize more accurately the nature of CNF-loaded samples, and indicate a higher flow resistance (Figure 4a) compared to that of pure SDS solutions. Figures 4b,c show that all samples containing CNF display a dominant elastic behavior (G' > G''). At the higher CNF concentration (1.5 wt %), the η*-values and the corresponding moduli are larger (Figure 4a-c). Additionally, it is apparent that

the presence of SDS (𝑐𝑆𝐷𝑆 ≥ cmc) strengthens the CNF network and enhances the elastic contribution (Figure 4b,c). We speculate that this is a result of SDS-induced CNF aggregation, which will be discussed later. Typically, samples with transient entanglements, such as those containing CNF, exhibit both shear thinning and extensional thickening.37 In fact, compared to pure SDS solutions (Figure 4d, open symbols), the presence of 0.3 wt % CNF (Figure 4d, filled symbols) significantly increases the extensional viscosity and Hencky strain (correlated with large three-dimensional deformations) against capillary thinning and breakup.



Figure 4. (a) Complex viscosity (η*), (b) storage (G', filled symbols) and loss (G'', patterned symbols) moduli as well as (c) loss tangent (tan δ = G''/G') for the respective systems as a function of the angular frequency (ω). The 0.3 and 1.5 wt % CNF-loaded samples are indicated with gray- and blue-filled symbols, respectively. (d) Extensional rheology (𝜂𝐸) as a function of Hencky strain (ɛHencky) for suspensions containing 0.3 wt % CNF (gray symbols) and SDS solutions (open symbols). From (a) to (d), circles denote pure CNF suspensions. Systems containing 0.7, 8.4, and 70 mM SDS are shown by triangle, square, and diamond symbols, respectively.

Electrostatic charge and colloid stability. As observed from the microscopy images of the respective suspensions (see insets in Figure 5a), SDS causes instability/phase separation of CNF in suspension.38 As will be discussed next, this is hypothesized to be due to charge screening and depletion-induced effects. Figure 5a shows the zeta potential and the conductivity of CNF suspensions as a function of the SDS concentration. A negative charge is recorded for the CNF 14 ACS Paragon Plus Environment

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suspension (see the zeta potential at 0 mM SDS in Figure 5a) which is caused by residual hemicelluloses (~ 25 wt % based on CNF dry mass) that exist on the surface of the fibrils (originally present in the fibers used to produce the CNF).39 Figure 5a also shows that SDS screens the repulsion between the negatively charged CNF surfaces, an effect being caused by the higher number density of Na+ counter-ions in the suspension and the increased ionic strength (reduced Debye length and electrostatic potential). The electrostatic charge becomes close to neutral at the highest SDS concentrations tested, which reduces the repulsion between the cellulose nanofibrils. Additionally, the like-charged CNF and SDS micelles cause exclusion of the latter from the zone between approaching fibrils, resulting in a concentration gradient of SDS micelles given their depletion relative to the bulk phase.40 As it is illustrated in Figure 5b, overlapping zones depleted of negatively charged micelles are formed between the negatively charged fibrils, causing an unbalanced osmotic pressure around the fibrils. As a result, an attractive depletion force is induced, causing the colloid instability and hence CNF aggregation (Figure 5a, inset microscopic images).



Figure 5. (a) Zeta potential (triangles) and conductivity (squares) of 0.3 wt % CNF suspensions in the presence of SDS at 0, 0.7, 8.4, and 70 mM. The destabilization of the CNF suspension at increasing SDS concentration is illustrated with the microscopy images added in the insets. The white scale bar in the images correspond to 200 µm. (b) Schematic illustration (not to scale) of the instability of charged CNF caused by the difference in osmotic pressure in the suspension as a result of depletion of SDS micelles between approaching CNF and fluid flow from the depletion zone to the surrounding areas. Note: CNF cross sections are drawn as circles, for simplicity.

Aqueous foams. Foam generation and stability. Figure 6 illustrates the effect of CNF (0.3 wt %) on the generation and decay of aqueous foams at three SDS concentrations, namely 0.7 mM (= 0.083 cmc), 8.4 mM (= cmc), and 70 mM (= 8.3 cmc). At a submicellar SDS concentration (0.083 cmc, Figure 6a, open gray symbols), the (maximum) set foam volume (120 mL) is reached after 964 s of continuous gas sparging in the SDS solution. The SDS foams decay immediately when the gas flow stops. This fast foam collapse is due to the insufficient replenishment of SDS molecules at the air/water interface. With the addition of CNF (0.3 wt %), the foam fails to reach the maximum volume (120 mL) (Figure 6a, yellow symbols). The inefficient foam generation of


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SDSaq+CNF at 0.7 mM SDS (𝑐𝑆𝐷𝑆 < cmc) is mainly ascribed to the limited availability of SDS molecules. Based on sensograms obtained from experiments using quartz crystal microgravimetry with dissipation monitoring (QCM-D) and surface plasmon resonance (SPR) (see Figure S2a-c), it can be concluded that SDS molecules interact with cellulosic fibers. The nature of the interactions is not fully clear but hydrophobic effects are possibly a major reason (see differential enthalpy isotherms in Figure S2d). SDS can also induce swelling (Figure S2a-c) and leaching of non-cellulosic components.27 A discussion on these topics is included in the Supporting Information (pages S2-S4). In short, the number of SDS unimers available is lower in the CNF suspension compared to that of pure 0.7 mM SDS, thus limiting foam generation. In addition, the leachate and the subsequently formed surface-active aggregates comprising leachate and SDS27 are not effective for SDSaq+CNF foam generation considering their hydrodynamic size.41 We note that the higher viscosity of the suspensions containing CNF does not affect the diffusion of SDS unimers, given the much larger mesh size of CNF network compared to the size of SDS molecules.41,42 For a pure SDS solution at 𝑐𝑆𝐷𝑆 ≥ cmc (Figure 6b,c, open gray symbols), the maximum foam volume is reached 10-fold faster (~72 s) compared to the time needed for a SDS solution at a submicellar concentration. Only a small decrease in foam volume (~20 mL) is observed within 33 min after stopping the gas flow. The SDS concentration-dependent foamability and foam stability of the solutions (Figure 6a vs Figure 6b,c) indicate the need for SDS molecular replenishment at the newly formed air/water interfaces. Distinctively, with the addition of CNF (0.3 wt %), the foams exhibit a similar foamability compared to that of pure SDS solutions at 𝑐𝑆𝐷𝑆 ≥ cmc (Figure 6b,c, t < 0 s). Due to the shear-thinning behavior of CNF-containing samples, the time needed for foaming (tfoaming) of pure SDS solutions and that of the SDSaq+CNF is about the same. In addition,



the lower air/water interfacial tension of SDSaq+CNF, compared to that of SDSaq (Figure 2b,d and Figure S1b,d), facilitates the fast deformation of the air/water interface in SDSaq+CNF foams. Moreover, due to the higher viscosity of SDSaq+CNF compared to the SDS solutions, the foam stability is improved in the presence of CNF (0.3 wt %) with a constant foam volume, Vfoam, observed over 33 min (Figure 6b,c, t  0 s). The influence of the viscosity on the improved foam stability will be discussed in detail in the following sections.

Figure 6. Time evolution of foam volume (Vfoam) of pure SDS solutions (open gray symbols) and SDS solutions containing 0.3 wt % CNF (SDSaq+CNF, yellow symbols). The concentration of SDS (𝑐𝑆𝐷𝑆 ) corresponds to (a) 0.7 mM, (b) 8.4 mM = cmc, and (c) 70 mM. The t = 0 s refers to the time at which the foam reaches the maximum set volume (Vfoam = 120 mL). At such time, the gas flow is stopped to observe the decay in foam’s volume.

Foam liquid fraction. Since SDSaq+CNF at 𝑐𝑆𝐷𝑆 < cmc does not reach the maximum set volume (Vfoam = 120 mL), the evolution of the liquid fraction () as a function of time was monitored only at 𝑐𝑆𝐷𝑆 ≥ cmc for pure SDS solutions and SDSaq+CNF. Thus, the associated foam stability and structure will be discussed at these SDS concentrations only. As can be seen from Figure 7a,b, the liquid fraction  for all foams decreases over time. Moreover,  of foams 18 ACS Paragon Plus Environment

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generated with SDSaq+CNF (SDS+CNF) is always higher than that produced from pure SDS (SDS) (Figure 7a-d). This is ascribed to the high “water-holding capability” of CNF43 (Figure S2) and its effect in producing a high complex viscosity (η*) and a predominating elastic behavior (tan δ < 1) (Figure 4a,c). These factors limit liquid drainage during foaming. Once foam generation stops, a higher apparent viscosity arises under the lower shear rate that exists in the continuous phase of the foam, producing a slower drainage (the CNF suspensions are shear-thinning and display a high zero-shear viscosity, Figure 3). Indeed, Figure S3 shows that the drainage rate (slope of the fitted profile at t < 100 s) of foams produced with SDSaq+CNF are lower than that for pure SDS solutions. We note that directly after foam generation, mainly drainage determines the foam stability. Thus, we consider the effect of drainage on foam properties only at short times, i.e. at t < 100 s in Figure S3. At long foam lifetimes, the lower drainage rates are also a result of the concentrated CNF in the foam nodes and plateau borders.



Figure 7. (a, b) Time evolution of the liquid fraction in the foams () for pure SDS solutions (open gray symbols) and for SDSaq+CNF (0.3 wt % CNF) (yellow symbols). (c, d) Cell size analysis (CSA) images of SDS foams (gray frames) and SDSaq+CNF foams (yellow frames) at t = 0 s and 1600 s. The scale bars in (c) and (d) correspond to 500 µm. The concentrations of SDS in (a, c) and (b, d) are 8.4 and 70 mM, respectively. (e) A fluorescence microscopy image of foams produced with SDSaq+CNF (𝑐𝑆𝐷𝑆 = 8.4 mM).

Figure 8 shows images of the foam columns at three distinct times of the experiment. A translucent layer of drained liquid is visible in the aged foam, which is formed between the bottom of the foam and the top of the aqueous phase or reservoir (Figure 8c). Compared to the opaque 0.3 wt % CNF suspension before foaming (Figure 8a), the translucent drained liquid illustrates that most CNF is retained in the foam (compare Figure 8b and c). Hence, if one assumes that all cellulose nanofibers become part of the foam at its initial stages (Figure 8b), it is reasonable to 20 ACS Paragon Plus Environment

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expect an increased CNF concentration in the foam’s continuous phase at long times, assuming that CNF-free water drained (Figure 8c). If that was the case, the CNF concentration in the liquid phase of the foam could increase up to 1.5 wt % at long times. Consequently, the viscosity of the continuous phase increases during aging (Figure 3 and 4a, from gray- to blue-filled symbols). It can be further argued that CNF is distributed non-homogeneously in the foam’s continuous phase due to fibril aggregation induced by depletion forces as discussed above in the context of Figure 5. Hence, a concentrated suspension containing CNF aggregates is present in the foam films and plateau borders, which may stabilize the foam (Figure 7c-e) and slow down drainage and coalescence, even at long foam lifetimes. Related phenomena have been observed in CNFstabilized multiphase systems, including Pickering emulsions21 and in SDS-stabilized films comprising cellulose nanocrystals.44

Figure 8. Photographs of FoamScan columns used for foam generation (8.4 mM SDS + 0.3 wt % CNF): (a) before foaming, (b) soon after foaming, (c) after 2100 s.

Aqueous foam structure. Figure 9 and Figure S4,5 show the bubble size evolution over time. Compared to foams produced from pure SDS solutions, those produced from SDSaq+CNF have a 21 ACS Paragon Plus Environment


larger average bubble size at the initial ( t = 0 s) and later (t = 1600 s) stages. The growth of and of the bubble size polydispersity (PDI) of SDSaq+CNF foams are slower than those in foams produced from pure SDS solutions. The onset of increase is shifted to longer foam lifetimes, namely from t ~ 400 for SDS foams to t ~ 800 s for SDSaq+CNF foams. The larger t = 0 s of SDSaq+CNF foams is a result of the lower air/water interfacial tension of SDSaq+CNF compared to that of SDSaq (Figure 2b,d), according to an equal total energy input 𝑈 = 4γ𝑟2. Where U is the total energy input,  is the air/water interfacial tension, and r is the radius of the bubbles.45 Although one may expect smaller t = 0 s for SDSaq+CNF foams, due to the higher bulk viscosity (Figure 4a-c) that acts against surface enlargement, the larger t = 0 s of SDSaq+CNF foams indicates the dominant role of air/water interfacial tension in determining the initial bubble size. The fact that the growth of starts after the change in the drainage rate (Figure S3) indicates that both coalescence and coarsening play a leading role in the late stages of the foam’s lifetime, while drainage dominates at the beginning. The dominating elastic behavior (Figure 4b,c) and high resistance to capillary breakup (Figure 4d) of the continuous phase make the SDSaq+CNF foam structure more stable. Moreover, the effect of capillary pressure is counter-balanced against coalescence.46 Coarsening caused by gas diffusion through foam films is driven by the difference in capillary pressure of adjacent bubbles. A growth in is expected (Figure 9, open gray symbols) together with the associated foam collapse (Figure 6b,c, open gray symbols). Apart from the contribution of the elasticity in the foam’s continuous phase, the elasticity of the air/water interface (Ed′) (Figure 2) reduces gas (nitrogen) permeability and thus limits coarsening of SDSaq+CNF foams (Figure 9).47–49


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Figure 9. Evolution of the arithmetic average bubble size of foams produced from SDS solutions (open gray symbols) and from SDSaq+CNF (0.3 wt % CNF, yellow symbols). The SDS concentrations are (a) 8.4 mM and (b) 70 mM. The polydispersity index (PDI) determined from 0 to 800 s in (a) and (b) is plotted in the insets. The PDI was recorded until 800 s due to the reduced number of bubbles captured by the CSA images at later times, limiting the statistical significance of the measurements (Figure S4 and S5).

CONCLUSIONS We studied (1) the colloidal stability and rheological behavior of unmodified cellulose nanofibrils (CNF) and their effect on properties of (2) the air/water interface and (3) the foams produced by SDS at different concentrations. The large axial aspect of the fibrils, their flexibility and hydration increase the viscosity of the bulk phase, with a predominant elastic behavior (tan δ < 1) even at a low CNF concentration (0.3 wt %). SDS causes CNF colloidal instability – i.e., aggregation – due to depletion effects. The air/water interfacial activity of SDSaq+CNF at 𝑐𝑆𝐷𝑆 ≥ cmc is higher than that of pure SDS solutions as a result of surface-active compounds that leach from CNF. At 𝑐𝑆𝐷𝑆 < cmc, the limited availability of surface-active molecules together with the 23 ACS Paragon Plus Environment


high viscosity of SDSaq+CNF prevents interfacial deformation and thus foam generation. However, the foaming efficiency of SDSaq+CNF is enhanced at 𝑐𝑆𝐷𝑆 ≥ cmc, given the accessible SDS molecules. More importantly, compared to pure SDS solutions, the SDSaq+CNF systems display a better foam stability due to a reduced drainage. This is in part a result of the shear-thinning effect of CNF. The stability of SDSaq+CNF foams also benefits from the enrichment of CNF aggregates in the foam’s plateau boarders and nodes. The extension-thickening effects in SDSaq+CNF and the predominant elastic behavior, both at the air/water interface and in the foam continuous phase, can effectively reduce coalescence (foam film thinning and rupture) and coarsening (bubble growth). Overall, this study furthers our current understanding of the effect of CNF in the generation and stabilization of aqueous foams produced by anionic surfactant solutions. The stabilizing mechanism imparted by CNF in foams produced by an anionic surfactant results from the improved bulk and interfacial rheology. Associated effects may be also relevant to foams produced with nonionic surfactants in the presence of electrolytes. However, in these cases surfactantinduced swelling and leaching of non-cellulosics from CNF may not occur.

SUPPORTING INFORMATION Air/water interfacial tension under oscillation; interaction between SDS and CNF studied by QCM-D, SPR, and ITC; foam’s liquid fraction; bubble size evolution over time.

ACKNOWLEDGMENTS

We acknowledge funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (ERC Advanced Grant agreement No 788489, “BioElCell”). The CLIC and SIRAF projects are also thanked for funding support. We 24 ACS Paragon Plus Environment

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appreciate the provision of facilities and technical assistance by Aalto University at OtaNanoNanomicroscopy Center (Aalto-NMC). We are grateful to Dr. Wiebke Drenckhan, from the Institut Charles Sadron (UPR22-CNRS), for helpful discussions. ITC measurements were facilitated by the generous support of Prof. Lasse Murtomäki, School of Chemical Engineering, Aalto University.

REFERENCE (1)

Huang, Z.; Su, M.; Yang, Q.; Li, Z.; Chen, S.; Li, Y.; Zhou, X.; Li, F.; Song, Y. Comm_A General Patterning Approach by Manipulating the Evolution of Two-Dimensional Liquid Foams. Nat. Commun. 2017, 8, 14110.

(2)

Löbmann, K.; Wohlert, J.; Müllertz, A.; Wågberg, L.; Svagan, A. J. Cellulose Nanopaper and Nanofoam for Patient-Tailored Drug Delivery. Adv. Mater. Interfaces 2017, 4 (9), 1600655. https://doi.org/10.1002/admi.201600655.

(3)

Rodríguez Patino, J. M.; Carrera Sánchez, C.; Rodríguez Niño, M. R. Implications of Interfacial Characteristics of Food Foaming Agents in Foam Formulations. Adv. Colloid Interface Sci. 2008, 140 (2), 95–113. https://doi.org/10.1016/j.cis.2007.12.007.

(4)

Li, S.; Xiang, W.; Järvinen, M.; Lappalainen, T.; Salminen, K.; Rojas, O. J. Interfacial Stabilization of Fiber-Laden Foams with Carboxymethylated Lignin toward Strong Nonwoven Networks. ACS Appl. Mater. Interfaces 2016, 8 (30), 19827–19835. https://doi.org/10.1021/acsami.6b06418.

(5)

Xiang, W.; Filpponen, I.; Saharinen, E.; Lappalainen, T.; Salminen, K.; Rojas, O. J. Foam Processing of Fibers As a Sustainable Alternative to Wet-Laying: Fiber Web Properties and Cause–Effect Relations. ACS Sustain. Chem. Eng. 2018, 6 (11), 14423–14431. https://doi.org/10.1021/acssuschemeng.8b03102.

(6)

Cervin, N. T.; Johansson, E.; Larsson, P. A.; Wågberg, L. Strong, Water-Durable, and WetResilient Cellulose Nanofibril-Stabilized Foams from Oven Drying. ACS Appl. Mater. Interfaces 2016, 8 (18), 11682–11689. https://doi.org/10.1021/acsami.6b00924.

(7)

Ali, Z. M.; Gibson, L. J. The Structure and Mechanics of Nanofibrillar Cellulose Foams. Soft Matter 2013, 9 (5), 1580–1588. https://doi.org/10.1039/c2sm27197d.

(8)

Svagan, A. J.; Benjamins, J.; Al-Ansari, Z.; Shalom, D. B.; Müllertz, A.; Wågberg, L.; 25 ACS Paragon Plus Environment


Page 26 of 31

Löbmann, K. Solid Cellulose Nanofiber Based Foams – Towards Facile Design of Sustained

Drug

Delivery

Systems.

J.

Control.

Release

2016,

244,

74–82.

https://doi.org/10.1016/j.jconrel.2016.11.009. (9)

Saint-Jalmes, A. Physical Chemistry in Foam Drainage and Coarsening. Soft Matter 2006, 2 (10), 836–849. https://doi.org/10.1039/b606780h.

(10)

Briceño-Ahumada, Z.; Langevin, D. On the Influence of Surfactant on the Coarsening of Aqueous

Foams.

Adv.

Colloid

Interface

Sci.

2017,

244,

124–131.

https://doi.org/10.1016/j.cis.2015.11.005. (11)

Binks, B. P. Particles as Surfactants - Similarities and Differences. Curr. Opin. Colloid Interface Sci. 2002, 7 (1–2), 21–41. https://doi.org/10.1016/S1359-0294(02)00008-0.

(12)

Hill, C.; Eastoe, J. Foams: From Nature to Industry. Adv. Colloid Interface Sci. 2017, 247, 496–513. https://doi.org/10.1016/j.cis.2017.05.013.

(13)

Rio, E.; Drenckhan, W.; Salonen, A.; Langevin, D. Unusually Stable Liquid Foams. Adv. Colloid Interface Sci. 2014, 205, 74–86. https://doi.org/10.1016/j.cis.2013.10.023.

(14)

Weaire, D.; Vaz, M. F.; Teixeira, P. I. C.; Fortes, M. A. Instabilities in Liquid Foams. Soft Matter 2007, 3 (1), 47–57. https://doi.org/10.1039/B608466B.

(15)

Langevin, D. Aqueous Foams and Foam Films Stabilised by Surfactants. Gravity-Free Studies.

Comptes

Rendus

-

Mec.

2017,

345

(1),

47–55.

https://doi.org/10.1016/j.crme.2016.10.009. (16)

Salonen, A.; In, M.; Emile, J.; Saint-Jalmes, A. Solutions of Surfactant Oligomers: A Model System for Tuning Foam Stability by the Surfactant Structure. Soft Matter 2010, 6 (10), 2271–2281. https://doi.org/10.1039/b924410g.

(17)

Green, A. J.; Littlejohn, K. A.; Hooley, P.; Cox, P. W. Formation and Stability of Food Foams and Aerated Emulsions: Hydrophobins as Novel Functional Ingredients. Curr. Opin. Colloid Interface Sci. 2013, 18 (4), 292–301. https://doi.org/10.1016/j.cocis.2013.04.008.

(18)

Murray, B. S.; Ettelaie, R. Foam Stability: Proteins and Nanoparticles. Curr. Opin. Colloid Interface Sci. 2004, 9 (5), 314–320. https://doi.org/10.1016/j.cocis.2004.09.004.

(19)

Lam, S.; Velikov, K. P.; Velev, O. D. Pickering Stabilization of Foams and Emulsions with Particles of Biological Origin. Curr. Opin. Colloid Interface Sci. 2014, 19 (5), 490–500. https://doi.org/10.1016/j.cocis.2014.07.003.

(20)

Abitbol, T.; Rivkin, A.; Cao, Y.; Nevo, Y.; Abraham, E.; Ben-Shalom, T.; Lapidot, S.; 26 ACS Paragon Plus Environment

Page 27 of 31 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

Biomacromolecules

Shoseyov, O. Nanocellulose, a Tiny Fiber with Huge Applications. Curr. Opin. Biotechnol. 2016, 39 (5), 76–88. https://doi.org/10.1016/j.copbio.2016.01.002. (21)

Bai, L.; Huan, S.; Xiang, W.; Rojas, O. J. Pickering Emulsions by Combining Cellulose Nanofibrils and Nanocrystals: Phase Behavior and Depletion Stabilization. Green Chem. 2018, 20 (7), 1571–1582. https://doi.org/10.1039/c8gc00134k.

(22)

Habibi, Y.; Lucia, L. A.; Rojas, O. J. Cellulose Nanocrystals: Chemistry, Self-Assembly, and

Applications.

Chem.

Rev.

2010,

110

(6),

3479–3500.

https://doi.org/10.1021/cr900339w. (23)

Lavoine, N.; Bergström, L. Nanocellulose-Based Foams and Aerogels: Processing, Properties, and Applications. J. Mater. Chem. A 2017, 5 (31), 16105–16117. https://doi.org/10.1039/c7ta02807e.

(24)

Bhattarai, M.; Pitkänen, L.; Kitunen, V.; Korpinen, R.; Ilvesniemi, H.; Kilpeläinen, P. O.; Lehtonen, M.; Mikkonen, K. S. Functionality of Spruce Galactoglucomannans in Oil-inWater

Emulsions.

Food

Hydrocoll.

2018,

1–8.

https://doi.org/10.1016/j.foodhyd.2018.03.020. (25)

Mikkonen, K. S.; Tenkanen, M.; Cooke, P.; Xu, C.; Rita, H.; Willför, S.; Holmbom, B.; Hicks, K. B.; Yadav, M. P. Mannans as Stabilizers of Oil-in-Water Beverage Emulsions. LWT - Food Sci. Technol. 2009, 42 (4), 849–855. https://doi.org/10.1016/j.lwt.2008.11.010.

(26)

Ogunkoya, D.; Li, S.; Rojas, O. J.; Fang, T. Performance, Combustion, and Emissions in a Diesel Engine Operated with Fuel-in-Water Emulsions Based on Lignin. Appl. Energy 2015, 154 (2015), 851–861. https://doi.org/10.1016/j.apenergy.2015.05.036.

(27)

Xiang, W.; Preisig, N.; Laine, C.; Hjelt, T.; Tardy, B. L.; Stubenrauch, C.; Rojas, O. J. Surface Activity and Foaming Capacity of Aggregates Formed between an Anionic Surfactant and Non-Cellulosics Leached from Wood Fibers. Biomacromolecules 2019, 20 (6), 2286–2294. https://doi.org/10.1021/acs.biomac.9b00243.

(28)

Nechyporchuk, O.; Belgacem, M. N.; Pignon, F. Current Progress in Rheology of Cellulose Nanofibril

Suspensions.

Biomacromolecules

2016,

17

(7),

2311–2320.

https://doi.org/10.1021/acs.biomac.6b00668. (29)

Mohtaschemi, M.; Sorvari, A.; Puisto, A.; Nuopponen, M.; Seppälä, J.; Alava, M. J. The Vane Method and Kinetic Modeling: Shear Rheology of Nanofibrillated Cellulose Suspensions. Cellulose 2014, 21 (6), 3913–3925. https://doi.org/10.1007/s10570-01427 ACS Paragon Plus Environment


Page 28 of 31

0409-x. (30)

Quennouz, N.; Hashmi, S. M.; Choi, H. S.; Kim, J. W.; Osuji, C. O. Rheology of Cellulose Nanofibrils in the Presence of Surfactants. Soft Matter 2016, 12 (1), 157–164. https://doi.org/10.1039/C5SM01803J.

(31)

Tardy, B. L.; Yokota, S.; Ago, M.; Xiang, W.; Kondo, T.; Bordes, R.; Rojas, O. J. Nanocellulose–Surfactant Interactions. Curr. Opin. Colloid Interface Sci. 2017, 29, 57–67. https://doi.org/10.1016/j.cocis.2017.02.004.

(32)

Clasen, C. Capillary Breakup Extensional Rheometry of Semi-Dilute Polymer Solutions. Korea-Australia Rheol. J. 2010, 22 (4), 331–338.

(33)

Nagel, M.; Tervoort, T. A.; Vermant, J. From Drop-Shape Analysis to Stress-Fitting Elastometry.

Adv.

Colloid

Interface

Sci.

2017,

247

(July),

33–51.

https://doi.org/10.1016/j.cis.2017.07.008. (34)

Cifuentes, A.; Bernal, J. L.; Diez-Masa, J. C. Determination of Critical Micelle Concentration Values Using Capillary Electrophoresis Instrumentation. Anal. Chem. 1997, 69 (20), 4271–4274. https://doi.org/10.1021/ac970696n.

(35)

Nazari, B.; Kumar, V.; Bousfield, D. W.; Toivakka, M. Rheology of Cellulose Nanofibers Suspensions: Boundary Driven Flow. J. Rheol. (N. Y. N. Y). 2016, 60 (6), 1151–1159. https://doi.org/10.1122/1.4960336.

(36)

Lundahl, M. J.; Berta, M.; Ago, M.; Stading, M.; Rojas, O. J. Shear and Extensional Rheology of Aqueous Suspensions of Cellulose Nanofibrils for Biopolymer-Assisted Filament

Spinning.

Eur.

Polym.

J.

2018,

109

(October),

367–378.

https://doi.org/10.1016/j.eurpolymj.2018.10.006. (37)

Patruyo, L. G.; Müller, A. J.; Sáez, A. E. Shear and Extensional Rheology of Solutions of Modified Hydroxyethyl Celluloses and Sodium Dodecyl Sulfate. Polymer (Guildf). 2002, 43 (24), 6481–6493. https://doi.org/10.1016/S0032-3861(02)00598-0.

(38)

Quennouz, N.; Hashmi, S. M.; Choi, H. S.; Kim, J. W.; Osuji, C. O. Rheology of Cellulose Nanofibrils in the Presence of Surfactants. Soft Matter 2016, 12 (1), 157–164. https://doi.org/10.1039/C5SM01803J.

(39)

Lou, Y.-R.; Kanninen, L.; Kuisma, T.; Niklander, J.; Noon, L. A.; Burks, D.; Urtti, A.; Yliperttula, M. The Use of Nanofibrillar Cellulose Hydrogel As a Flexible ThreeDimensional Model to Culture Human Pluripotent Stem Cells. Stem Cells Dev. 2014, 23 28 ACS Paragon Plus Environment

Page 29 of 31 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

Biomacromolecules

(4), 380–392. https://doi.org/10.1089/scd.2013.0314. (40)

Tuinier, R.; Rieger, J.; De Kruif, C. G. Depletion-Induced Phase Separation in ColloidPolymer

Mixtures.

Adv.

Colloid

Interface

Sci.

2003,

103

(1),

1–31.

https://doi.org/10.1016/S0001-8686(02)00081-7. (41)

Jowkarderis, L.; van de Ven, T. G. M. Mesh Size Analysis of Cellulose Nanofibril Hydrogels Using Solute Exclusion and PFG-NMR Spectroscopy. Soft Matter 2015, 11 (47), 9201–9210. https://doi.org/10.1039/C5SM01752A.

(42)

Danov, K. D.; Basheva, E. S.; Kralchevsky, P. A.; Ananthapadmanabhan, K. P.; Lips, A. The Metastable States of Foam Films Containing Electrically Charged Micelles or Particles: Experiment and Quantitative Interpretation. Adv. Colloid Interface Sci. 2011, 168 (1–2), 50–70. https://doi.org/10.1016/j.cis.2011.03.006.

(43)

De France, K. J.; Hoare, T.; Cranston, E. D. Review of Hydrogels and Aerogels Containing Nanocellulose.

Chem.

Mater.

2017,

29

(11),

4609–4631.

https://doi.org/10.1021/acs.chemmater.7b00531. (44)

Tardy, B. L.; Ago, M.; Guo, J.; Borghei, M.; Kämäräinen, T.; Rojas, O. J. Optical Properties of Self-Assembled Cellulose Nanocrystals Films Suspended at Planar-Symmetrical Interfaces. Small 2017, 13 (47), 1702084. https://doi.org/10.1002/smll.201702084.

(45)

Drenckhan, W.; Saint-Jalmes, A. The Science of Foaming. Adv. Colloid Interface Sci. 2015, 222, 228–259. https://doi.org/10.1016/j.cis.2015.04.001.

(46)

Bey, H.; Wintzenrieth, F.; Ronsin, O.; Höhler, R.; Cohen-Addad, S. Stabilization of Foams by the Combined Effects of an Insoluble Gas Species and Gelation. Soft Matter 2017, 13 (38), 6816–6830. https://doi.org/10.1039/c6sm02191c.

(47)

Martinez, A. C.; Rio, E.; Delon, G.; Saint-Jalmes, A.; Langevin, D.; Binks, B. P. On the Origin of the Remarkable Stability of Aqueous Foams Stabilised by Nanoparticles: Link with

Microscopic

Surface

Properties. Soft

Matter

2008,

4

(7),

1531–1535.

https://doi.org/10.1039/b804177f. (48)

Stocco, A.; Drenckhan, W.; Rio, E.; Langevin, D.; Binks, B. P. Particle-Stabilised Foams: An

Interfacial

Study.

Soft

Matter

2009,

5

(11),

2215–2222.

https://doi.org/10.1039/b901180c. (49)

Alvarez, N. J.; Anna, S. L.; Saigal, T.; Tilton, R. D.; Walker, L. M. Interfacial Dynamics and Rheology of Polymer-Grafted Nanoparticles at Air-Water and Xylene-Water Interfaces. 29 ACS Paragon Plus Environment


Langmuir 2012, 28 (21), 8052–8063. https://doi.org/10.1021/la300737p.


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