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Adaptation of a Styrene-Acrylic Acid Copolymer Surface to Water.

ABSTRACT: Solid surfaces, in particular polymer surfaces, are able to adapt upon contact with a liquid. Adaptation results in an increase in contact angle hysteresis and influences the mobility of sliding drops on surfaces. To study adaptation and its kinetics, we synthesized a random copolymer composed of styrene and 11-25 mol% acrylic acid (PS/PAA). We measured the dynamic advancing (?_A) and receding (?_R) contact angles of water drops sliding down a tilted plate coated with this polymer. We measured ?_A ? 87° for velocities of the contact line <20 ?m/s. At higher velocities, ?_A gradually increased to ?98°. This value is similar to ?_A of a pure polystyrene (PS) film, which we studied for comparison. We associate the gradual increase in ?_A to the adaptation process to water: The presence of water leads to swelling and/or an enrichment of acid groups at the water/polymer interface. By applying the latest adaptation theory (Butt et al. Langmuir 2018, 34, 11292), we estimated the time constant of this adaptation process to be ?1 s. For sliding water drops, ?_R is ?10° lower compared to the reference PS surface for all tested velocities. Thus, at the receding side of a sliding drop, the surface is already enriched by acid groups. For a water drop with a width of 5 mm, the increase in contact angle hysteresis corresponds to an increase in capillary force in the range of 45-60 ?N, depending on sliding velocity.

SUBMITTER: Li X

PROVIDER: S-EPMC7880564 | biostudies-literature | 2021 Feb

REPOSITORIES: biostudies-literature

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Adaptation of a Styrene-Acrylic Acid Copolymer Surface to Water.

Li Xiaomei X Silge Simon S Saal Alexander A Kircher Gunnar G Koynov Kaloian K Berger Rüdiger R Butt Hans-Jürgen HJ

Langmuir : the ACS journal of surfaces and colloids 20210113 4

Solid surfaces, in particular polymer surfaces, are able to adapt upon contact with a liquid. Adaptation results in an increase in contact angle hysteresis and influences the mobility of sliding drops on surfaces. To study adaptation and its kinetics, we synthesized a random copolymer composed of styrene and 11-25 mol% acrylic acid (PS/PAA). We measured the dynamic advancing (θ<sub>A</sub>) and receding (θ<sub>R</sub>) contact angles of water drops sliding down a tilted plate coated with this po ...[more]

PMID: 33439030

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Project description:The membrane-embedded protein rhodopsin is widely produced in organisms as a photoreceptor showing a variety of light-dependent biological functions. To investigate its molecular features, rhodopsin is often extracted from cellular membrane lipids by a suitable detergent as "micelles." The extracted protein is purified by column chromatography and then is often reconstituted into "liposomes" by removal of the detergent. The styrene-maleic acid ("SMA") copolymer spontaneously forms nanostructures containing lipids without detergent. In this study, we applied SMA to characterize two microbial rhodopsins, a thermally stable rhodopsin, Rubrobacter xylanophilus rhodopsin (RxR), and an unstable one, Halobacterium salinarum sensory rhodopsin I (HsSRI), and evaluated their physicochemical properties in SMA lipid particles compared with rhodopsins in micelles and in liposomes. Those two rhodopsins were produced in Escherichia coli cells and were successfully extracted from the membrane by the addition of SMA (5 w/v %) without losing their visible color. Analysis by dynamic light scattering revealed that RxR in SMA lipid particles (RxR-SMA) formed a discoidal structure with a diameter of 54 nm, which was 10 times smaller than RxR in phosphatidylcholine liposomes. The small particle size of RxR-SMA allowed us to obtain scattering-less visible spectra with a high signal-to-noise ratio similar to RxR in detergent micelles composed of n-dodecyl-β-D-maltoside. High-speed atomic force microscopy revealed that a single particle contained an average of 4.1 trimers of RxR (12.3 monomers). In addition, RxR-SMA showed a fast cyclic photoreaction (k = 13 s-1) comparable with RxR in phosphatidylcholine liposomes (17 s-1) but not to RxR in detergent micelles composed of n-dodecyl-β-D-maltoside (0.59 s-1). By taking advantage of SMA, we determined the dissociation constant (Kd) of chloride for HsSRI as 34 mM. From these results, we conclude that SMA is a useful molecule forming a membrane-mimicking assembly for microbial rhodopsins having the advantages of detergents and liposomes.

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Adaptation of a Styrene-Acrylic Acid Copolymer Surface to Water.

Publications

Adaptation of a Styrene-Acrylic Acid Copolymer Surface to Water.

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