Pickering Membranes Stabilized by Saturn Particles - Langmuir (ACS

Subscriber access provided by - Access paid by the | UCSB Libraries

Article

Pickering Membranes Stabilized by Saturn Particles Matthias Michael Krejca, Cornell Wüstner, and Werner A. Goedel Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.7b01852 • Publication Date (Web): 07 Sep 2017 Downloaded from http://pubs.acs.org on September 8, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Langmuir is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 30

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

Pickering Membranes Stabilized by Saturn Particles Matthias M. Krejca, Cornell Wüstner, Werner A. Goedel*

Physical Chemistry, Institute of Chemistry, Chemnitz University of Technology, Straße der Nationen 62, 09111 Chemnitz, Germany *Corresponding author. Email: [email protected]

1 ACS Paragon Plus Environment

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 2 of 30

ABSTRACT We report on a novel method to synthesize particles –called by us Saturn particles - having two hydrophobic caps that oppose each other and are separated from each other by a hydrophilic belt that encircles the particle. Mixtures of these particles with water and air, without the usage of low molar mass surfactants, easily form Pickering foams and Pickering membranes that are stable for days. These Pickering membranes are composed of a thin film of water into which the particles are embedded in such a way that the belt is surrounded by the water and the caps protrude out of the water into the air at the top and bottom side of the water film. As expected for a liquid membrane, these Pickering membranes are permeable for gases – the permeance being proportional to the solubility and diffusion coefficient of the gas considered. Experimentally obtained permeance values agree reasonably well with theoretical calculations.

air

water

100 µm

Keywords: Saturn Particle, Pickering Membrane, Particle-Stabilized Foam, Permeance


Page 3 of 30

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

INTRODUCTION As described by S. U. PICKERING in 19071 and observed before by W. RAMSDEN in 19032, particles spontaneously adsorb to the surface of droplets and may be used to prepare dispersions (often called Pickering emulsions) of liquids in liquids, liquids in gases, or gases in liquids (see Figure 1a). These emulsions can be used, for example, for cosmetics,3 material sciences,4 emulsion polymerization,5 dry foams,6 or even as encapsulation systems for drug delivery.7 They often have an extraordinary long time stability, which can be attributed to the relative high energy associated with the adsorption or desorption of a particle to a fluid interface.8,9 This high energy of adsorption is due to the area of the interface of the droplet that is replaced by the particle and the sheer size of the particle, which of course is quite tiny but still a manifold of the size of low molar mass surfactants.9 The energy of adsorption is especially strong, if the contact angle between the particle surface and the surface of the liquid droplet is close to 90 °.10 Thus, there are formulations of Pickering emulsions that include low molar mass surfactants to tune this contact angle.11 As an alternative way to achieve a suitable contact angle, one might choose a suitable combination of particles and liquid or chemically modify the particle surface and thus create stable Pickering emulsions that are surfactant-free.12 Usually, the particles used are uniform and do not pose any kind of amphiphilic structure. The formation of Pickering emulsions can be enhanced further by giving the particles a hydrophilic and hydrophobic region (such particles are called Janus particles13). These particles arrange themselves preferably at interfaces between two non-miscible fluids (see Figure 1b).14–17,18,23


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

Figure 1. Pickering emulsions a) with homogeneous particles, b) with Janus particles; Pickering membrane c) double layer membrane with homogeneous particles, d) monolayer membrane with homogeneous particles, e) Pickering monolayer membrane with Saturn particles. (I) obtained with predominantly hydrophobic particles and (II) obtained with with predominantly hydrophilic particles; red color indicates hydrophobic properties, blue color indicates hydrophilic properties

So far particles were successfully used to form emulsions, replacing amphiphilic molecules. Nature uses amphiphilic molecules as well for the spontaneous formation of membranes and vesicles. Therefore, it is an interesting and maybe even useful exercise to try forming so called Pickering membranes that is membranes consisting solely of particles and liquids. Such membranes can be stabilized via various mechanisms.27 The most common stabilization occurs is when two droplets of a Pickering emulsion – each one surrounded by a dense monolayer of particles – come into contact. The drainage of the fluid between the droplets can result in a membrane that is made of two particle layers touching each other in the middle of the membrane and each partially imbibed in a thin film of the fluid that originally surrounded the emulsion droplets and partially protruding out into an adjacent fluid that originally formed the droplets (see Figure 1c).28 If the lateral density of particles on the surface of the original droplets is low enough, one may as well observe the formation of a membrane in which the particles form a monolayer within a thin film of one fluid. In this type of membrane, each particle bridges the film of the fluid within the membrane and each particle protrudes out of the mem4 ACS Paragon Plus Environment

Page 4 of 30

Page 5 of 30

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

brane into the adjacent fluid on both interfaces of the membrane(see Figure 1d).29–31. In these two cases, the particles must be located mostly in the interior phase of the membranes formed. Thus, the contact angle of the fluid within the membrane to the particle, θ(particle / fluid within the membrane / fluid adjacent to the membrane), must be smaller than 90 °.10,27 On the other hand, the particles need a strong adhesion to the interface to prohibit being pushed out. Thus, the contact angle shall not be too low either. Another mechanism to form stable bilayers between droplets or bubbles is the adsorption of particles followed by a formation of a rigid network.6,32,33 This rigidity slows down the displacement of particles from the interface, regardless of the contact angle. In nature, membranes often are formed with a bilayer of amphiphilic molecules,34 mostly phospholipids35; the particle-stabilized bilayer membrane sketched in Figure 1c and described in literature28 resembles such membranes. Some kinds of bacteria, so called archaea bacteria – and especially the ones that live under extreme environmental conditions36–, have a special kind of membrane: a monolayer membrane of bipolar amphiphilic lipids with two head groups that protrude out of the membrane at opposing sides, connected to each other by a backbone that bridges the membrane (so called archaeal lipids).37 Our idea uses the lipid monolayer of some archaea bacteria as an inspiration. Compared to Janus particles, we increase the number of regions on the surface of the particles by one and obtain particles with three regions: two opposing caps that are hydrophobic and a hydrophilic region (the belt) that separates them – or vice versa: the caps may be hydrophilic and the belt hydrophobic. We call these particles Saturn particles, referring to a Roman god, as previously was done in the case of the Janus particles, and at the same time to the planet Saturn with the belt-like rings (other authors call them triblock Janus38 or patchy particles39). By using such particles, we should be able to stabilize preferentially membranes instead of spherical droplets. We thus set out to synthesize Saturn particles and therefrom particle-stabilized Pickering membranes as sketched in Figure 1e.


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

EXPERIMENTAL SECTION Materials Ethanol, acetone, hydrogen peroxide (50 %), sulfuric acid, and toluene were technical grade,

n-octadecyltriethoxysilane (ODES) (95 %) was purchased from abcr GmbH Karlsruhe, 3methacryloxypropyltrimethoxysilane (TPM) (97 %) was purchased from Alfa Aesar Haverhill, Kraton G1650E was obtained from NRC Nordmann Rassmann GmbH Hamburg as a gift, hydrofluoric acid (40 %) was purchased from AppliChem GmbH Darmstadt, carbon dioxide (99.995 %) was purchased from Air Liquide Deutschland GmbH Düsseldorf, sulfur hexafluoride (99.9 %) was purchased from Praxair Inc. Düsseldorf, glass particles (Glass Beads 75 um) were purchased from Supelco St. Louis. The mean diameter of the glass beads varied from batch to batch. In the case of particles that were in a first step homogeneously coated by treatment with n-octadecyltriethoxysilane and subsequently used for the preparation of Saturn particles we used a batch of mean diametre of dparticle = 76.2 µm , √ = 4.9 µm (obtained by measuring from scanning electron microscopy images the diametres of 1000 particles and calculating the arithmetic mean value) . In the case of particles homogeneously coated by treatment with 3-methacryloxypropyltrimethoxysilane the mean diametre was dparticle’

= 82.4 µm, √ = 4.2 µm (obtained by measuring from scanning electron microscopy im-

ages the diametres of 128 particles and calculating the arithmetic mean value). Gellan gum was purchased from AppliChem GmbH Darmstadt, Sylgard 184 Silicone Elastomer was purchased from Dow Corning GmbH Midland, ultra-pure water (conductivity = 0.054 µS/cm², TOC = 1 ppb) was prepared using a TKA Smart2Pure by JWT GmbH Jena. All chemicals were used as received.

Hydrophobic Coating of the Glass Particles To coat glass particles with a silane, about 5 g of the particles were placed into a standard 100 mL glass Erlenmeyer flask with ground joint and washed with denatured ethanol and dried. A freshly prepared 2:1 mixture of sulfuric acid and hydrogen peroxide at a temperature of approximately 60 °C that is achieved due to the heat of mixing was added until every particle was covered. The Erlenmeyer flask was shaken in intervals of approximately 5 minutes for a period of an hour and allowed to cool down to room temperature within that period. The particles were filtered off using a glass frit and washed with water until the wash water was neutral. Subsequently, the particles were dried in an oven at 70 °C. A mixture of 50 mL dried toluene (dried by molecular sieve 4A activated by heating to 250 °C for 2 h) and 0.1 mL of silane (n-octadecyltriethoxysilane or 3-methacryloxypropyltrimethoxysilane) was added to the 6 ACS Paragon Plus Environment

Page 6 of 30

Page 7 of 30

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

particles, the atmosphere above the mixture was replaced by nitrogen, and the Erlenmeyer flask was sealed with a Teflon lined ground glass stopper. It was shaken with a laboratory shaker for 1 day in the case of methacryloxypropyltrimethoxysilane and for 49 days in the case of n-octadecyltriethoxysilane at a frequency of 1.7 Hz and a lateral amplitude of 1.5 cm. Afterwards, the particles were washed with toluene, acetone, and denatured ethanol. The particles were finally dried and stored in dryness.

Preparation of Saturn Particles An etching cell was constructed from two polymethylmethacrylate (PMMA) rectangular cuboids. Top and bottom side of the cuboids had the dimensions 4 cm wide × 6 cm long, and the cuboids had a height of 1.5 cm. Each of the cuboids had 8 through bores, running from top to bottom parallel to the 1.5 cm edge. Close to each of the 6 cm × 1.5 cm sides, there were four bores with a distance to the 6 cm × 1.5 cm side of 6 mm. and a distance to each other of 16 mm. 8 M4x40 screws that were placed within these bores, together with 8 nuts, allowed to press the bottom side of the upper cuboid to the top side of the lower cuboid. In addition, the upper cuboid had two through bores running from top to bottom parallel to the 1.5 cm edge, each of them at a distance of 7 mm to one of the 4 cm × 1.5 cm sides and both at a distance of 20 mm to the 6 cm × 1.5 cm sides. These two bores were used as inlet and outlet for the etching and washing liquids. Between the top side of the lower cuboid and the bottom side of the upper cuboid, we placed two 4 cm × 6 cm Kraton G1650E foils of 1.2 mm thickness and between these two foils a Teflon spacer of 50 µm thickness. The center of the Teflon spacer was cut out in the shape of two circular arcs of opposing curvature, meeting at the location of the inlet and outlet for the fluids and having a radius of curvature of 3 cm (see as well Supporting Information Figure S2 and Figure S3). In order to generate the Saturn particles, the lower cuboid was covered with the lower Kraton foil, which was covered by the Teflon spacer. A monolayer

of

glass

particles

hydrophobically

coated

by

treatment

with

n-

octadecyltriethoxysilane was sprinkled onto the lower Kraton foil within the cut-out central opening of the Teflon spacer. The top Kraton foil was put on top of the particle monolayer and the spacer. The top cuboid was placed on top of the second Kraton foil, and the PMMA cuboids (and thus, the Kraton foils) were pressed together by screwing the nuts onto the screws using a torque of 0.60 Nm on each nut. 1 mL of diluted hydrofluoric acid (0.63 mol/L) was pumped through the slit in between the Kraton foils at a volumetric flow rate of 0.1 mL/min for 10 min. (Caution! Hydrofluoric acid is toxic, extremely corrosive, hazardous,

and shall be handled with care and by trained personnel only!) Afterwards, 1 mL of diluted 7 ACS Paragon Plus Environment

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

hydrofluoric acid of the same concentration was pumped through in reverse direction through the slit between the foils at the same flow rate for the same time. Finally, the particles were rinsed by pumping 10 mL of water through the slit at a volumetric flow rate of 0.1 mL/min for 100 min. The top PMMA cuboid was removed, and the particles were rinsed off the foils with ethanol. The ethanol was evaporated and the Saturn particles were stored in dryness.

Pickering Membrane Creation A tapered glass u-tube (see Figure 5 and Supporting Information Figure S4) was filled with a few milliliters of ultra-pure water. Particles were added until the tapered part of the u-tube was filled with particles at the bottom. Two air bubbles were carefully pumped through the pump side of the u-tube in quick succession. This created a Pickering membrane in the riser side of the u-tube.

Permeance Measurement The pump side of the tapered glass u-tube with a created Pickering membrane on the riser side was sealed with a plug. A gas container was filled with a gas (carbon dioxide or sulfur hexafluoride) and mounted onto the riser side of the u-tube. Initially, the gas inside the container was separated from the gas above the Pickering membrane via a closed valve (valve A). The interior pressure of the gas container and the pressure above the Pickering membrane were equilibrated with the surrounding atmospheric pressure via an additional valve (valve B). This setup was placed into a temperature-controlled box. Inside this box were a thermometer and an electronic camera. After the whole construction was thermostated to 298 K, valve A was opened and the serial recording of pictures in intervals of 5 minutes began. To expose the upper side of the Pickering membrane to air again, the gas container was removed from the utube.

Contact Angle Measurement Round glass cover slips were treated the same way as the used glass particles. For the contact angle measurement of glass cover slips, the contact angle measurement device G2 by Krüss and the evaluation software Drop Shape Analysis DSA II by Krüss were used. Two glass cover slips were taken and 10 measurements of advancing and receding contact angles were performed for every treatment. The measurements were averaged and the errors given are the standard deviation from the mean value. For the contact angle measurement of the particles that were hydrophobically coated by treatment with n-octadecyltriethoxysilane, a monolayer of particles was sprinkled onto a 8 ACS Paragon Plus Environment

Page 8 of 30

Page 9 of 30

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

60 °C warm 2.0 wt% aqueous solution of Gellan gum.40 After cooling to room temperature and waiting for a day, PDMS Sylgard 184 elastomer (mixing ratio base : curing agent of 10:1) was poured on top of the Gellan gum solution. After waiting for 2 days, the PDMS was peeled off and washed with hot water. Pictures were taken via a scanning electron microscope and the angles α(particle/air (replacing the water phase)/PDMS) of 60 particles were measured by human judgement with ImageJ (W. S. Rasband, ImageJ, U. S. National Institutes of Health, Bethesda, Maryland, USA, https://imagej.nih.gov/ij/, 1997–2017.).


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 10 of 30

RESULTS AND DISCUSSION As discussed in the introduction, we want to use Saturn particles to stabilize liquid Pickering membranes (in absence of low molar mass amphiphiles). In the following, we first describe the preparation of the Saturn particles and then the Pickering membrane formation.

Preparation of Saturn Particle

hydrophobize with ODES

press between two foils

etch with HF

flush with H2O

harvest

Figure

2.

Schematic

illustration

of

the

preparation


of

the

Saturn

particles.

Page 11 of 30

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

The process of preparing Saturn particles is schematically depicted in Figure 2. First, glass particles are hydrophobized via the reaction with n-octadecyltriethoxysilane (ODES). Then a monolayer of particles is pressed in between two thermoplastic elastomer foils kept at 50 µm distance by a surrounding non-elastic spacer foil. The elastomer foil masks the caps of the particles. Diluted hydrofluoric acid is pumped through the remaining free volume between the particles, followed by water. The hydrofluoric acid etches away a few micrometers of the glass beads and at the same time removes the hydrophobic coating. This procedure leads to the desired Saturn particles. In contrast to most other methods which create the three different surface regions of Saturn particles in a variety of steps,41–43 this method can create the three different surface regions in one single step.

detched dparticle wetched

Figure 3. Scanning Electron Microscope (SEM) picture of Saturn particles. The height of the particle, dparticle, as well as the height, detched, and width, wetched, of the etched belt is drawn into the picture. The used glass particles originally are spherical (see Supporting Information Figure S1a) and have a number average diameter of dparticle = 76.2 µm (√ = 4.9 µm). After etching, the belt of the Saturn particles has an average height of detched = 52.2 µm (√ = 7.9 µm, arithmetic mean based on images of 158 particles). This average height correlates well with the thickness of the used Teflon spacer of 50 µm. The etching primarily is done to render the belt hydrophilic, at the same time it reduces the width of the particles across the belt to an average value of wetched = 68.5 µm (√ = 3.9 µm, arithmetic mean based on images of 200 particles). Furthermore, the etching creates pits and dents on the glass surface. In order to harvest a sufficient number of particles for the experiments reported here and for other purposes, we repeat11 ACS Paragon Plus Environment

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 12 of 30

ed the etching procedure for more than 40 times. We observe variations in the results smaller than the standard deviations given above – as long as the geometrical parameters of the components of the equipment and the materials they are made of are not changed. The etched belt stands in a high hydrophobicity contrast to the caps. To obtain an estimate of this contrast, glass cover slips were coated with ODES and etched for the same period of time as the particles were. The etched glass cover slips showed contact angles to the water/air interface

θ(cover

slip/water/air)advancing = 31.0 °

(√ = 6.8 °)

and

θ(cover

slip/water/air)receding = 10.3 ° (√ = 2.8 °). The coated glass cover slips showed contact angles to water in air of θ(cover slip/water/air)advancing = 89.3 ° (√ = 3.4 °) and θ(cover slip/water/air)receding = 73.4 ° (√ = 11.78°). For comparison the contact angles of the hydrophobically coated particles were determined by PAUNOV’s gel trapping technique.40 The coated particles showed contact angles to water in air of θ(particle/water/air) = 91.3 ° (√ = 9.6 °). The value thus obtained is identical to the value of the coated cover slips within the experimental error. This latter fact gives us confidence that the contact angle of the used liquids on glass cover slips are suitable to judge contact angles on particles. Glass cover slips coated with 3-methacryloxypropyltrimethoxysilane (TPM) showed contact angles to water in air of θ(cover slip/water/air)advancing = 50.6 ° (√ = 2.2 °) and θ(cover slip/water/air)receding = 39.2 ° (√ = 2.4 °).

Pickering Foam and Pickering Membranes When uniform spherical glass particles, hydrophobized via n-octadecyltriethoxysilane (ODES) (but not etched at the belt) are suspended in ultra-pure water in a vessel in addition with air and if this vessel is shaken vigorously, their ability to stabilize bubbles is negligible. The ability to stabilize bubbles increases if instead of the very hydrophobic ODES a silane of intermediate hydrophobicity, 3-methacryloxypropyltrimethoxysilane, is used as surface coating for the spherical particles. Membranes that are stable for at least several minutes can be achieved by blowing air into a suspension of these particles in water. Images of such Pickering membranes are shown in Figure 4a) and in Figure S10 in the Supporting Information and suggest that the Pickering membrane thus formed is of the monolayer type sketched in Figure 1d. (The truncated spherical structures that are visible above and to some extent below the particles in panel a) we interpret as reflection images at the water/air interface of the meniscus.)


Page 13 of 30

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

If the Saturn particles are shaken with air and water, a foam is formed. In contrast to Pickering foams reported in the literature,6,28,32,44 we observe the formation of rather large foam cells – in the size of several millimeters to centimeters in diameter. Often, five to twenty bubbles are formed, which sometimes even coalesce into a single one. This foam is stable over weeks, even though it does not contain low molar mass surfactants. A side view onto one lamella of such a foam is shown in Figure 4b, an overview image in Figure S9 in the Supporting Information. a) air

water

b) air

water

Figure 4. Light microscopic image of a single Pickering membrane in side view (the rim of the membrane that touches the glass wall of the container), stabilized a) by homogeneously coated particles of intermediate hydrophobicity and b) by Saturn particles.45 The sketch of the particle on the left was added to schematically demonstrate the structure of a Pickering membrane. Water surrounds the hydrophilic belt of the Saturn particles and connects them. The hydrophobic caps are not wetted by the water but instead protrude into the hydrophobic air. In contrast to other particle-stabilized foams, this Pickering foam does not have to have densely packed layers of particles on both air-water-surfaces28,46 or highly entangled particle shells to create a long-term stabilized foam.6,32,33 In the literature, bridging particles often are described 13 ACS Paragon Plus Environment

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 14 of 30

as useful agents to initiate a rupture of metastable lamellae via the bridging-dewetting mechanism.47 When the contact angle θ(particle/liquid film /outer phase ) is above 90 °, the threephase contact lines move towards the interior until both contact lines meet and the film ruptures. If this angle is below 90 °, one can observe the opposite.48 Here, the use of Saturn particles makes the Pickering membrane extraordinarily stable. We attribute this stability to the fact that the water-air-particle three-phase contact line is pinned at the transition zone between the hydrophobic cap and the hydrophilic belt. Thus, as we hoped for in the introduction, Saturn particles easily stabilize liquid Pickering membranes – even in membrane diameters exceeding 1 cm in diameter. This enables us to prepare a single Pickering membrane and to further characterize its properties.

Permeance of a Pickering Membrane In nature as well as in technological applications, one of the most important properties of a membrane is its permeability and selectivity for substances that may pass or be blocked from passing. In our Pickering membrane that is composed of pure water and Saturn particles, water is the only component that allows permeation of substances. Therefore, we expect a permeability of components through the Pickering membrane that shall depend on the diffusion constant and solubility of the components in water.

Theoretical Permeances The permeance of a membrane for a given gas, i, is defined as the molar amount, dni, that flows through an area, A, of a membrane within a given time interval, dt, at a given partial pressure difference between feed and permeate side of the membrane, ∆pi .

Permeance = −

∆

∙ ∆

=− ∙

Equation 1

The theoretical Permeance of a homogeneous liquid membrane for a given gas, i, is giv

en by the product of the Diffusion coefficient, , times the Henry’s constant, , divided by the thickness of the membrane, d.49 Permeance =

∙ "

Equation 2

This equation is valid as well for aqueous soapy membranes thicker than 20–30 nm; for a soapy membrane of a thickness of 26 nm for example one can calculate from Equation 2 a theoretical permeance of about 400·10-9 mol m-2Pa-1s-1 to 600·10-9 mol m-2Pa-1s-1 14 ACS Paragon Plus Environment

50

and

Page 15 of 30

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

experimentally51 observes a value of 260·10-9 mol m-2Pa-1s-1

52

(only if the thickness de-

creases down to common or newton black films, the permeance becomes dominated by the flow resistance imposed by the surfactant monolayers that cover both sides of the membrane). In a simplified picture that neglects the curvature of the belt, we may describe our Pickering membrane as a densely packed array of vertically oriented impermeable cylinders of height

detched embedded in a permeable liquid film of thickness detched. The cylinders occupy an area fraction of #

√$

#

√$

.54 Thus, the water film occupies an effective area fraction of %&& = 1 −

. To obtain the permeance through this Pickering membrane, Permeance , ( , we have to

multiply Equation 2 by the effective area fraction and obtain: Permeance , ( =

∙ ∙ %&& "

Equation 3

Theoretical permeances thus calculated for various gases are listed in Table 1.


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

Page 16 of 30

Table 1. Diffusion coefficients and Henry’s constants (concentration in solution / partial pressure in gas phase 55) of various gases in water at T = 298 K and theoretical permeances calculated for a Pickering membrane of a thickness of 52 µm and an effective area of 1 −

#

. Numbers in

√$

square brackets indicate the reference the value was taken from. N2 diffusion coefficient )* [m² s ] -1

a

b

-9

[56]

-6

[55,60]

2.0110

Henry’s Constant +,- [mol m ³ Pa ] -2 -1 -1 b theoretical permeance ./01/23,/45/6 *,-1 [mol m Pa s ] -

-1

O2

6.410 2.2910-11

-9

[56]

-5

[55]

2.2010

1.210 4.7110-11

a

Ar

Air -9

[57]

-5

[55]

1.4410

1.410 3.5910-11

The theoretical permeance of air is the average of the theoretical permeances weighted by their natural volume fraction in air: Permeance . 7 8 = 0.78 Permeance= > + 0.21 PermeanceA> + 0.01 PermeanceB8 Calculated via Equation 3.

16

ACS Paragon Plus Environment

CO2 [58]

-4

[55,61]

1.9410 2.8110-11

SF6

-9

3.310 11410-11

1.2010-9

[59]

-6

[55]

2.410 0.5110-11

Page 17 of 30

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

Langmuir

Table 2. Permeance differences of two types of Pickering membranes for two pairs of gases.

gas pair 2 Saturn particles

Pickering Membrane stabilized by … 2homogeneously coated spherical g particles

experiment [mol m-2 Pa-1 s-1]

a -11

CO2 – air

(Permeance CO2 − Permeance air)exp

68.4 10 -11 ± 4.5810

air – SF6

(Permeance air − exp Permeance SF6)

2.7610-11 ± 0.2010-11 -11 42.0 10 -11 ± 11.910

CO2 – air air – SF6

(Permeance CO2 − Permeance air) exp (Permeance air − exp Permeance SF6)

Permeance differences theory [mol m-2 Pa-1 s-1]

3.2810-11

c

d

Permeance CA2, ( – Permeance 7 8, ( Permeance 7 8, ( – Permeance DE6, (

b

experiment/theory

11110

-11

0.61

2.3010-11

1.20

e

f

a

calculated from the maximum speed of the membrane via Equation 6 calculated from the values listed in Table 1 c Mean value and standard deviation for carbon dioxide for the cycles shown in Table S1 in the Supporting Information. d Mean value and standard deviation for the experiment shown in Figure 9 and the two additional experiments in Figure S6 in the Supporting Information. e Mean value and standard deviation for the experiment shown in Figure S11 and Figure S12 in the Supporting Information. f Single measurement value for the experiment shown in Figure S13 and Figure S14 in the Supporting Information. g Coated by treatment with 3-methacryloxypropyltrimethoxysilane. b

17


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

Experimentally Obtained Permeance Differences

Container for CO2 or SF6 (not drawn in scale) Valve A Valve B

Joint

Pump tube Riser tube Pickering membrane

Ultra-pure water

Figure 5. Tapered u-tube for the creation of a Pickering membrane. Spherical particles homogeneously coated with n-octadecyltriethoxysilane (ODES) or 3methacryloxypropyltrimethoxysilane (TPM) or Saturn particles are added to water in a tapered glass u-tube (see Figure 5; for a photo of the setup see Supporting Information Figure S4 and Figure S5). Air bubbles are pumped through the pump tube of the u-tube into the water (valve B open). These bubbles rise to the water surface in the riser tube. ODES coated particles predominantly stay on the water surface. The air bubble breaks through this layer of floating particles and immediately bursts in the same way as it does at a water surface in absence of particles. Spherical particles homogeneously coated with TPM as well as Saturn particles predominantly sediment to the bottom of the u-tube. The bubble passing this sediment collects a part of the sedimented particles and transports them to the water surface. A Pickering membrane is formed there spontaneously, lifts off, and rises up further in the riser tube by additionally pumped air. This gives rise to a horizontally oriented circular Pickering membrane; its rim clings to the wall of the riser tube; above and below it is air. We observe that the 18 ACS Paragon Plus Environment

Page 18 of 30

Page 19 of 30

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

Pickering membrane formed by the Saturn particles is significantly more robust than the Pickering membrane formed by the homogeneously coated spherical particles. The Pickering membrane formed by the Saturn particles survives the following permeation experiments for times longer than a day and needs longer times to dry if exposed to dry air. To characterize the permeances of these membranes for various gases, we replace the air above the Pickering membrane by another gas by opening the valve A and shortly afterwards closing valve B. After opening valve A the atmosphere above the Pickering membrane differs from the one below. Thus, gases permeate through the Pickering membrane driven by osmosis. If the Pickering membrane has a higher permeance for the gas above than for the gas below, it will rise (and vice versa). In the first series of experiments, we choose carbon dioxide as the gas for replacing the air above the Pickering membrane. Carbon dioxide has a significantly higher theoretical permeance than air (see Table 1). Permeation of Carbon Dioxide A Pickering membrane is created in the riser tube. Then the valve A is opened and the air above the Pickering membrane is replaced with carbon dioxide. Since carbon dioxide is denser than air, it diffuses quickly down the riser to the Pickering membrane and then diffuses through it. As expected the membrane rises; the movement of the Pickering membrane stabilized by Saturn particles is shown in photographs in Figure 6 and plotted versus time in a graph in Figure 7. The corresponding data for a membrane stabilized by homogeneously coated spherical particles are shown in Figure S11 and Figure S12 in the Supporting Information. As can be seen in Figure 7, the movement needs approximately ten minutes to pick up speed, most probably the time needed for completing the gas exchange above the Pickering membrane and inversion of the curvature of the membrane (which is visible in Figure 6). It then seems to proceed with constant speed. In theory, it should slow down again as the partial t = 1700 min

t = 1715 min

t = 1730 min

t = 1765 min

t = 1805 min

air

CO2

CO2

air

air

a)

air

b)

air + CO2

c)

air + CO2

d)

air + CO2

e)

air

Figure 6. The permeation of carbon dioxide through a Pickering membrane stabilized by Saturn particles. The cycle shown in this figure is the 11th one in Figure 7. The carbon dioxide above the Pickering membrane permeates through it (b–c), causing an upward movement. The carbon dioxide is replaced by air after 1730 min. The carbon dioxide below the Pickering membrane perme19 ates back through the Pickering membrane until there is only air left (d–e), causing a downward movement. Scale bar is 2 mm.


Langmuir

pressure of carbon dioxide below the Pickering membrane increases. However, we do not wait for this effect and completely remove the gas container and open the top of the riser tube to air. As the riser tube is opened to the air, we observe that the Pickering membrane sinks again, according to our expectations, as the carbon dioxide above the Pickering membrane is replaced by air and the carbon dioxide below the Pickering membrane diffuses back. This movement is slower than the first movement because the atmosphere below the Pickering membrane is not pure carbon dioxide but a mixture of it with air. This experiment can be repeated several times over a period of more than a day with one and the same Pickering membrane (see Figure 7). An animation composed of all pictures taken during the experiment can be found in the Supporting Information (see Supporting Information Figure S7). We conclude from the repeated movement of the Pickering membrane that it was intact for almost 32 h.

CO2

16

air height [mm]

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 20 of 30

15

14

13

12

0

200

400

600

800

1000

1200

1400

1600

1800

2000

time [min]

Figure 7. Height of the Pickering membrane stabilized by Saturn particles above the water level in the riser tube over time. Full squares indicate a carbon dioxide atmosphere above the Pickering membrane, empty squares indicate the ventilated state with air above the Pickering membrane. The Pickering membrane broke down after 12 cycles (1910 minutes). At daytime, the height of the Pickering membrane was measured every 5 minutes. In the extended overnight period (minute 880–1450) the height of the Pickering membrane was measured every 30 minutes. Dashed line: switching from carbon dioxide to air. Dotted line: switching from air to carbon dioxide.


Page 21 of 30

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

To compare the theoretical permeances with experiments, we may calculate the permeance difference from the speed of the movement of the Pickering membrane. The speed of the movement, GH , is equal to the volumetric flux. Assuming that air and carbon dioxide behave as ideal gases at room temperature, T, and atmospheric pressure, patm , we obtain: GH = −

I

= −

RK

Latm

∙N

OP>

+

QRS

T .

Equation 4

Using the definition of the permeance, we obtain: GH =

RK

Latm

∙ N∆LCO ∙ PermeanceCA> + ∆L%WX ∙ Permeance7 8 T . 2

Equation 5

At the start of each cycle, we may assume further that the partial pressure of carbon dioxide above the Pickering membrane is equal to the atmospheric pressure, L7( , and is zero below and we may assume reverse conditions for the air. Thus, the difference in partial pressure of air, ∆L7 8 , and the difference in partial pressure of carbon dioxide, ∆LCA> , have the same absolute value as the atmospheric pressure and opposite sign: ( ∆LCA> ≈ L7( ≈ −∆L7 8 ). Thus, we obtain for the membrane speed the approximation: ZPermeanceCO2 − Permeanceair \

]

G

0 = ^∙K .

Equation 6

As discussed above, the Pickering membrane needs some time to pick up speed. Thus, we used the maximum speed obtained from the filled squares in Figure 7 to calculate the experimental permeance difference via Equation 6 . (The simplification ∆LCA> ≈ L7( cannot be made for the part of the cycle when the carbon dioxide above the Pickering membrane is replaced by air and the carbon dioxide below diffuses back.) We list the values obtained via Equation 6 in Table 2 and compare them to the ones calculated from Henry’s constants and diffusion coefficient via Equation 3. Given the simplicity of our experimental setup and of our mathematical model, the experimental values compare to our satisfaction to the theoretical ones. Reasons for the deviation of the experimental permeance differences to the ones calculated from Henry’s constants may be: the Pickering membrane moves with friction to the glass tube wall; carbon dioxide dissolves in the water below the Pickering membrane, which diminishes the increase of the gas volume between the Pickering membrane and the water reservoir. We observe that the permeance of the membranes stabilized by homogeneously coated spherical particles are similar to the permeances stabilized by the Saturn particles. Thus, it seems 21 ACS Paragon Plus Environment

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

likely, that the thickness of the aqueous part of these membranes and the volume fraction occupied by the particles of these membranes are comparable to the ones stabilized by Saturn particles. This interpretation is supported further by the image of the membrane seen from the side. However, it is obvious from the curved surfaces of the spherical particles that the actual diffusion paths have to differ from our simple model. Thus, for this type of Pickering membrane we do not include a comparison to the theory into Table 2. Permeation of Air Sulfur hexafluoride is an inorganic gas which is denser than air and, in contrast to carbon dioxide, very badly soluble in water. Thus, we expect that the permeance of the Pickering membrane for this gas is much lower than for air. In the second series of experiments, the air above the Pickering membrane was in a first cycle replaced by carbon dioxide, which was then replaced by air again. This was done to ensure by comparison with the experiments before that the Pickering membrane was intact. Then the air above the Pickering membrane was replaced by sulfur hexafluoride. We expected that air permeated through the Pickering membrane much slower than carbon dioxide but much faster than sulfur hexafluoride and thus a sinking of the membrane with air below and SF6 above it and indeed observed a movement in the expected direction. The movement of the Pickering membrane stabilized by Saturn particles is shown in photographs in Figure 8 and plotted versus time in a graph in Figure 9. Additional experiments are shown in Figure S6 in the Supporting Information. An animation composed of all pictures taken during the experiment can be found in the Supporting Information (see Supporting Information Figure S8). The corresponding data for a membrane stabilized by homogeneously coated spherical particles are shown in Figure S13 and Figure S14 in the Supporting Information.


Page 22 of 30

Page 23 of 30

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

Langmuir

t = 0 min

t = 30 min

air

a)

air

t = 155 min

t = 730 min

t = 1365 min

t = 1410 min

t = 1520 min

air

SF6

CO2

CO2

air

CO2

b)

air + CO2

c)

air

d)

air

e)

air

f)

air + CO2

g)

air

Figure 8. The movement of a Pickering membrane stabilized by Saturn particles due to the permeation of different gases through it. The air above the Pickering membrane is replaced by carbon dioxide. The carbon dioxide above the Pickering membrane permeates through it (b). The carbon dioxide is replaced by air after 30 min. The carbon dioxide below the Pickering membrane permeates back through the Pickering membrane until there is only air left (c). The air above the Pickering membrane is replaced by sulfur hexafluoride. The air below the Pickering membrane permeates through the Pickering membrane and the Pickering membrane sinks (d–e). After 1365 min, the sulfur hexafluoride is replaced by carbon dioxide (e). The Pickering membrane rises (f) and, after the carbon dioxide is replaced by air, the Pickering membrane sinks (g) again. Scale bar is 2 mm.

23


Langmuir

CO2

CO2

air

22

SF6

air

CO2 air SF6

21 20

height [mm]

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 24 of 30

19 18 17 16 15 14 0

200

400

600

800

1000

1200

1400

1600

time [min]

a) b) c)

d)

e) f) g)

Figure 9. Height of the Pickering membrane stabilized by Saturn particles above the water level in the riser tube over time. The height of the Pickering membrane was measured every 5 minutes. When the atmosphere above the Pickering membrane was replaced by sulfur hexafluoride, the height of the Pickering membrane was measured every 30 minutes. Full squares indicate a carbon dioxide atmosphere, white squares indicate the ventilated state with air above the Pickering membrane, and crossed red squares indicate sulfur hexafluoride above the Pickering membrane. The vertical lines show the moment the atmosphere above the Pickering membrane was exchanged. The arrows below the abscissa indicate the time at which the images a) to g) from Figure 8 were taken.


Page 25 of 30

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

Next, the sulfur hexafluoride above the Pickering membrane was replaced by carbon dioxide to check whether the Pickering membrane was still intact. First, the carbon dioxide had to replace the sulfur hexafluoride above the Pickering membrane before the permeation began significantly. Because of this, it took some additional time before the curvature of the Pickering membrane changed and the Pickering membrane finally rose. After the carbon dioxide above the Pickering membrane was replaced by air again, the Pickering membrane sank again and broke down 26 hours after the experiment started. Again, we took the permeances of both gases in opposite directions into account, calculated the permeance difference from Equation 6 and listed the resulting value in Table 2. As in the case of the gas pair air/carbon dioxide, the experimental permeance difference of SF6 to air is not in perfect but reasonably good agreement to the theoretically calculated one.

CONCLUSION Inspired by the bipolar lipids of the membranes of special archaea bacteria, we were able to create Pickering membranes, stabilized by Saturn particles. These Pickering membranes are stable for time spans exceeding a day. They comprise a liquid film as continuous phase and thus are mobile and show selective permeances for components soluble in this liquid part.

Acknowledgments The authors are grateful to Frank Diener from the metal-workshop of Chemnitz University of Technology for manufacturing the PMMA cuboids, and to Ursula Zimmermann from the glass-blowing workshop of Chemnitz University of Technology for manufacturing the tapered u-tube. We thank M. Hietschold, S. Schulze, and D. Dentel from Chemnitz University of Technology (Chair of Solid Surface Analysis) for helping in obtaining the SEM images. We thank H. Langenau for programming the camera program. This work was financed by the Deutsche Forschungsgemeinschaft (DFG).

Supporting Information SEM image of the used spherical glass particles; photos of the etching device, of the experimental setup for permeance measurements and overview images of Pickering membranes; experimental values of permeance differences before averaging, animated images of the two main experiments. 25 ACS Paragon Plus Environment

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

REFERENCES (1) (2)

(3)

(4)

(5)

(6)

(7)

(8) (9) (10) (11)

(12) (13)

(14)

(15) (16)

(17)

Pickering, S. U. CXCVI.—Emulsions. J Chem Soc Trans 1907, 91 (0), 2001–2021. DOI: 10.1039/CT9079102001 Ramsden, W. Separation of Solids in the Surface-Layers of Solutions and “Suspensions” (Observations on Surface-Membranes, Bubbles, Emulsions, and Mechanical Coagulation). — Preliminary Account. Proc. R. Soc. Lond. 1903, 72 (477–486), 156–164. DOI: 10.1098/rspl.1903.0034 Gers-Barlag, H.; Müller, A. Emulsifier-Free Finely Disperse Systems of the Oil-inWater and Water-in-Oil Type. US6803049 B2, registered April 25. 2002, released October 12. 2004. Arditty, S.; Schmitt, V.; Giermanska-Kahn, J.; Leal-Calderon, F. Materials Based on Solid-Stabilized Emulsions. J. Colloid Interface Sci. 2004, 275 (2), 659–664. DOI: 10.1016/j.jcis.2004.03.001 Chen, T.; Colver, P. J.; Bon, S. A. F. Organic–Inorganic Hybrid Hollow Spheres Prepared from TiO2-Stabilized Pickering Emulsion Polymerization. Adv. Mater. 2007, 19 (17), 2286–2289. DOI: 10.1002/adma.200602447 Menner, A.; Verdejo, R.; Shaffer, M.; Bismarck, A. Particle-Stabilized Surfactant-Free Medium Internal Phase Emulsions as Templates for Porous Nanocomposite Materials: Poly-Pickering-Foams. Langmuir 2007, 23 (5), 2398–2403. DOI: 10.1021/la062712u Simovic, S.; Hui, H.; Song, Y.; Davey, A. K.; Rades, T.; Prestidge, C. A. An Oral Delivery System for Indomethicin Engineered from Cationic Lipid Emulsions and Silica Nanoparticles. J. Controlled Release 2010, 143 (3), 367–373. DOI: 10.1016/j.jconrel.2010.01.008 Binks, B. P.; Lumsdon, S. O. Stability of Oil-in-Water Emulsions Stabilised by Silica Particles. Phys. Chem. Chem. Phys. 1999, 1 (12), 3007–3016. DOI: 10.1039/a902209k Binks, B. P. Particles as Surfactants—similarities and Differences. Curr. Opin. Colloid Interface Sci. 2002, 7 (1–2), 21–41. DOI: 10.1016/S1359-0294(02)00008-0 Dickinson, E. Food Emulsions and Foams: Stabilization by Particles. Curr. Opin. Colloid Interface Sci. 2010, 15 (1–2), 40–49. DOI: 10.1016/j.cocis.2009.11.001 Binks, B. P.; Rodrigues, J. A.; Frith, W. J. Synergistic Interaction in Emulsions Stabilized by a Mixture of Silica Nanoparticles and Cationic Surfactant. Langmuir 2007, 23 (7), 3626–3636. DOI: 10.1021/la0634600 Sakai, T. Surfactant-Free Emulsions. Curr. Opin. Colloid Interface Sci. 2008, 13 (4), 228–235. DOI: 10.1016/j.cocis.2007.11.013 Casagrande, C.; Fabre, P.; Raphaël, E.; Veyssié, M. “Janus Beads”: Realization and Behaviour at Water/Oil Interfaces. Europhys. Lett. EPL 1989, 9 (3), 251–255. DOI: 10.1209/0295-5075/9/3/011 Binks, B. P.; Fletcher, P. D. I. Particles Adsorbed at the Oil−Water Interface: A Theoretical Comparison between Spheres of Uniform Wettability and “Janus” Particles. Langmuir 2001, 17 (16), 4708–4710. DOI: 10.1021/la0103315 Kim, J.-W.; Lee, D.; Shum, H. C.; Weitz, D. A. Colloid Surfactants for Emulsion Stabilization. Adv. Mater. 2008, 20 (17), 3239–3243. DOI: 10.1002/adma.200800484 Tanaka, T.; Okayama, M.; Minami, H.; Okubo, M. Dual Stimuli-Responsive “Mushroom-like” Janus Polymer Particles as Particulate Surfactants. Langmuir 2010, 26 (14), 11732–11736. DOI: 10.1021/la101237c Fujii, S.; Yokoyama, Y.; Miyanari, Y.; Shiono, T.; Ito, M.; Yusa, S.; Nakamura, Y. Micrometer-Sized Gold–Silica Janus Particles as Particulate Emulsifiers. Langmuir 2013, 29 (18), 5457–5465. DOI: 10.1021/la400697a


Page 26 of 30

Page 27 of 30

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

(18) Apart from the stabilization of emulsions, there are various fields of applications for Janus particles like switchable displays,19 self-motile particles20, biomarkers21, or magnetolytic tumor therapy22. (19) Nisisako, T.; Torii, T.; Takahashi, T.; Takizawa, Y. Synthesis of Monodisperse Bicolored Janus Particles with Electrical Anisotropy Using a Microfluidic Co-Flow System. Adv. Mater. 2006, 18 (9), 1152–1156. DOI: 10.1002/adma.200502431 (20) Howse, J. R.; Jones, R. A. L.; Ryan, A. J.; Gough, T.; Vafabakhsh, R.; Golestanian, R. Self-Motile Colloidal Particles: From Directed Propulsion to Random Walk. Phys. Rev. Lett. 2007, 99 (4), 048102. DOI: 10.1103/PhysRevLett.99.048102 (21) Yoshida, M.; Roh, K.-H.; Mandal, S.; Bhaskar, S.; Lim, D.; Nandivada, H.; Deng, X.; Lahann, J. Structurally Controlled Bio-Hybrid Materials Based on Unidirectional Association of Anisotropic Microparticles with Human Endothelial Cells. Adv. Mater. 2009, 21 (48), 4920–4925. DOI: 10.1002/adma.200901971 (22) Hu, S.-H.; Gao, X. Nanocomposites with Spatially Separated Functionalities for Combined Imaging and Magnetolytic Therapy. J. Am. Chem. Soc. 2010, 132 (21), 7234– 7237. DOI: 10.1021/ja102489q (23) Pickering emulsions can be transformed into capsules as shown in reference 24 reference 25 and reference 26. (24) Velev, O. D.; Furusawa, K.; Nagayama, K. Assembly of Latex Particles by Using Emulsion Droplets as Templates. 1. Microstructured Hollow Spheres. Langmuir 1996, 12 (10), 2374–2384. DOI. 10.1021/la9506786 (25) Huck, W. T. S.; Tien, J.; Whitesides, G. M. Three-Dimensional Mesoscale SelfAssembly. J. Am. Chem. Soc. 1998, 120 (32), 8267–8268. DOI: 10.1021/ja981390g (26) Dinsmore, A. D.; Hsu, M. F.; Nikolaides, M. G.; Marquez, M.; Bausch, A. R.; Weitz, D. A. Colloidosomes: Selectively Permeable Capsules Composed of Colloidal Particles. Science 2002, 298 (5595), 1006–1009. DOI: 10.1126/science.1074868 (27) Lopetinsky, R. J. G.; Masliyah, J. H.; Xu, Z. Solids-Stabilized Emulsions: A Review. In Colloidal Particles at Liquid Interfaces; Binks, B. P., Horozov, T. S., Eds.; Cambridge University Press: Cambridge, 2006; pp 186–224. DOI: 10.1017/CBO9780511536670.007 (28) Fujii, S.; Iddon, P. D.; Ryan, A. J.; Armes, S. P. Aqueous Particulate Foams Stabilized Solely with Polymer Latex Particles. Langmuir 2006, 22 (18), 7512–7520. DOI: 10.1021/la060812u (29) Horozov, T. S.; Aveyard, R.; Clint, J. H.; Neumann, B. Particle Zips: Vertical Emulsion Films with Particle Monolayers at Their Surfaces. Langmuir 2005, 21 (6), 2330–2341. DOI: 10.1021/la047993p (30) Horozov, T. S.; Binks, B. P. Particle-Stabilized Emulsions: A Bilayer or a Bridging Monolayer? Angew. Chem. Int. Ed. 2006, 45 (5), 773–776. DOI: 10.1002/anie.200503131 (31) Stancik, E. J.; Fuller, G. G. Connect the Drops: Using Solids as Adhesives for Liquids. Langmuir 2004, 20 (12), 4805–4808. DOI: 10.1021/la049778e (32) Alargova, R. G.; Warhadpande, D. S.; Paunov, V. N.; Velev, O. D. Foam Superstabilization by Polymer Microrods. Langmuir 2004, 20 (24), 10371–10374. DOI: 10.1021/la048647a (33) Wege, H. A.; Kim, S.; Paunov, V. N.; Zhong, Q.; Velev, O. D. Long-Term Stabilization of Foams and Emulsions with In-Situ Formed Microparticles from Hydrophobic Cellulose. Langmuir 2008, 24 (17), 9245–9253. DOI: 10.1021/la801634j (34) Gorter, E.; Grendel, F. On Bimolecular Layers of Lipoids on the Chromocytes of the Blood. J. Exp. Med. 1925, 41 (4), 439–443. DOI: 10.1084/jem.41.4.439 (35) Wilkins, M. H. F.; Blaurock, A. E.; Engelman, D. M. Bilayer Structure in Membranes. Nature. New Biol. 1971, 230 (11), 72–76. DOI: 10.1038/newbio230072a0 27 ACS Paragon Plus Environment

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 28 of 30

(36) Hanford, M. J.; Peeples, T. L. Archaeal Tetraether Lipids: Unique Structures and Applications. Appl. Biochem. Biotechnol. 2002, 97 (1), 45–62. DOI: 10.1385/ABAB:97:1:45 (37) Langworthy, T. A. Long-Chain Diglycerol Tetraethers from Thermoplasma Acidophilum. Biochim. Biophys. Acta BBA - Lipids Lipid Metab. 1977, 487 (1), 37–50. DOI: 10.1016/0005-2760(77)90042-X (38) Chen, Q.; Bae, S. C.; Granick, S. Directed Self-Assembly of a Colloidal Kagome Lattice. Nature 2011, 469 (7330), 381–384. DOI: 10.1038/nature09713 (39) Zhang; Glotzer, S. C. Self-Assembly of Patchy Particles. Nano Lett. 2004, 4 (8), 1407– 1413. DOI: 10.1021/nl0493500 (40) Paunov, V. N. Novel Method for Determining the Three-Phase Contact Angle of Colloid Particles Adsorbed at Air−Water and Oil−Water Interfaces. Langmuir 2003, 19 (19), 7970–7976. DOI: 10.1021/la0347509 (41) Jiang, S.; Granick, S. A Simple Method to Produce Trivalent Colloidal Particles. Langmuir 2009, 25 (16), 8915–8918. DOI: 10.1021/la902152n (42) Lin, C.-C.; Liao, C.-W.; Chao, Y.-C.; Kuo, C. Fabrication and Characterization of Asymmetric Janus and Ternary Particles. ACS Appl. Mater. Interfaces 2010, 2 (11), 3185–3191. DOI: 10.1021/am1006589 (43) Zhao, Z.; Shi, Z.; Yu, Y.; Zhang, G. Ternary Asymmetric Particles with Controllable Patchiness. Langmuir 2012, 28 (5), 2382–2386. DOI: 10.1021/la203654h (44) Du, Z.; Bilbao-Montoya, M. P.; Binks, B. P.; Dickinson, E.; Ettelaie, R.; Murray, B. S. Outstanding Stability of Particle-Stabilized Bubbles. Langmuir 2003, 19 (8), 3106– 3108. DOI: 10.1021/la034042n (45) Wüstner, C. Selbstorganisierte Strukturen Mit Saturn-Partikeln; Dissertation; Technische Universität Chemnitz: Chemnitz, 2014. (46) Gonzenbach, U. T.; Studart, A. R.; Tervoort, E.; Gauckler, L. J. Ultrastable ParticleStabilized Foams. Angew. Chem. Int. Ed. 2006, 45 (21), 3526–3530. DOI: 10.1002/anie.200503676 (47) Aveyard, R.; Binks, B. P.; Fletcher, P. D. I.; Rutherford, C. E. Contact Angles in Relation to the Effects of Solids on Film and Foam Stability. J. Dispers. Sci. Technol. 1994, 15 (3), 251–271. DOI: 10.1080/01932699408943557 (48) Horozov, T. Foams and Foam Films Stabilised by Solid Particles. Curr. Opin. Colloid Interface Sci. 2008, 13 (3), 134–140. DOI: 10.1016/j.cocis.2007.11.009 (49) Mulder, M. Basic Principles of Membrane Technology; Springer Netherlands: Dordrecht, 1996, p 235. ` (50) Literature51 gives the permeability coefficient K = ∙ a with ∆(n/V) being the dif∙B ∆N T b

ference in molar concentration between feed and permeate. To convert this equation into permeances as defined by Equation 1 we have to divide both sides by the ideal gas constant, R, and the temperature, T. Using this conversion, a temperature of 298 K and the theoretical value given for Ki = 0.1 cm/s from the literature51, we obtain a permeance for air of approximately 400·10-9 mol m-2Pa-1s-1 , using the values for the Henry’s constant and diffusion coefficient of Table 1, we obtain from Equation 3 a theoretical value of 600·10-9 mol m-2Pa-1s-1 . (51) Farajzadeh, R.; Muruganathan, R. M.; Rossen, W. R.; Krastev, R. Effect of Gas Type on Foam Film Permeability and Its Implications for Foam Flow in Porous Media. Adv. Colloid Interface Sci. 2011, 168 (1–2), 71–78. DOI: 10.1016/j.cis.2011.03.005 (52) Calculated by dividing the value of Ki = 0.064 cm/s extracted out of reference 51 (Fig. 6) or reference 53 (Figure 5) by R and by T. (53) Farajzadeh, R.; Krastev, R.; Zitha, P. L. J. Gas Permeability of Foam Films Stabilized by an α-Olefin Sulfonate Surfactant. Langmuir 2009, 25 (5), 2881–2886. DOI: 10.1021/la803599z 28 ACS Paragon Plus Environment

Page 29 of 30

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

(54) Tóth, L. F. Some Packing and Covering Theorems. Acta Sci Math Szeged 1950, 12, 62– 67. (55) Sander, R. Compilation of Henry’s Law Constants (Version 4.0) for Water as Solvent. Atmospheric Chem. Phys. 2015, 15 (8), 4399–4981. DOI: 10.5194/acp-15-4399-2015 (56) Ferrell, R. T.; Himmelblau, D. M. Diffusion Coefficients of Nitrogen and Oxygen in Water. J. Chem. Eng. Data 1967, 12 (1), 111–115. DOI: 10.1021/je60032a036 (57) Maharajh, D. M.; Walkley, J. The Temperature Dependence of the Diffusion Coefficients of Ar, CO2, CH4, CH3Cl, CH3Br, and CHCl2F in Water. Can. J. Chem. 1973, 51 (6), 944–952. DOI: 10.1139/v73-140 (58) Tamimi, A.; Rinker, E. B.; Sandall, O. C. Diffusion Coefficients for Hydrogen Sulfide, Carbon Dioxide, and Nitrous Oxide in Water over the Temperature Range 293-368 K. J. Chem. Eng. Data 1994, 39 (2), 330–332. DOI: 10.1021/je00014a031 (59) King, D. B.; Saltzman, E. S. Measurement of the Diffusion Coefficient of Sulfur Hexafluoride in Water. J. Geophys. Res. 1995, 100 (C4), 7083–7088. DOI: 10.1029/94JC03313 (60) Warneck, P.; Williams, J. The Atmospheric Chemist’s Companion; Springer Netherlands: Dordrecht, 2012. DOI: 10.1007/978-94-007-2275-0 (61) Sander, S. P.; Abbatt, J.; Barker, J. R.; Burkholder, J. B.; Friedl, R. R.; Golden, D. M.; Huie, R. E.; Kolb, C. E.; Kurylo, M. J.; Moortgat, G. K.; et al. Chemical Kinetics and Photochemical Data for Use in Atmospheric Studies Evaluation Number 17, JPL Publication 10-6, Jet Propulsion Laboratory, Pasadena, 2011, http://jpldataeval.jpl.nasa.gov (accessed June 1, 2017).


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

air

water

100 µm

TOC


Page 30 of 30

Pickering Membranes Stabilized by Saturn Particles - Langmuir (ACS

Recommend Documents