Temperature Dependence of the Surface and Volume Hydrophilicity of Hydrophilic Polymer Brushes

Abstract

The temperature-dependence of the volume and surface hydrophilicity of a series of water-swollen dense polymer brushes is measured by contact angle measurements in the captive bubble configuration, by ellipsometry, and by quartz crystal microbalance with dissipation monitoring (QCM-D). Thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) and poly(di(methoxyethoxy)ethyl methacrylate) (PMEO2MA), strongly hydrophilic poly(N,N-dimethylacrylamide) (PDMA) and poly(oligo(ethylene glycol) methacrylate) (POEGMA), and weakly hydrophilic poly(2-hydroxyethyl methacrylate) (PHEMA) brushes were synthesized by surface-initiated atom-transfer radical polymerization (SI-ATRP). Conditions leading to reproducible measurements of the contact angle are first provided, giving access to the surface hydrophilicity. Volume hydrophilicity is quantified by measuring the swelling of the brushes, either by QCM-D or by ellipsometry. A model-free methodology is proposed to analyze the QCM-D data. Comparison between the acoustic and optical swelling coefficients shows that QCM-D is sensitive to the maximal thickness of swollen brushes, while ellipsometry provides an integral thickness. Diagrams of surface versus volume hydrophilicity of the brushes finally lead to identify two types of behavior: strongly water-swollen brushes exhibit a progressive decrease of volume hydrophilicity with temperature, while surface hydrophilicity changes moderately; weakly water-swollen brushes have a close-to-constant volume hydrophilicity, while surface hydrophilicity decreases with temperature. Thermoresponsive brushes abruptly switch from one behavior to the other, and do not exhibit an abrupt change of surface hydrophilicity across their collapse transition contrarily to a common erroneous belief. In general, there is no direct correlation between surface and volume hydrophilicity, because surface properties are dependent on the details of conformation and composition at the surface, whereas volume properties are averaged over a finite region within the brush.

Thin Poly(Di(Ethylene Glycol)Methyl Ether Methacrylate) Homopolymer Brushes Allow Controlled Adsorption and Desorption of PaTu 8988t Cells

“…The dependence of the angle shift due to irreversibly adsorbed proteins and molecules in the cell medium versus temperature can be described in both cases by a sigmoid function, in analogy to the previously reported BSA experiments . The inflection points of 32 ± 2 °C for fibronectin (Figure c) and 29 ± 2 °C for cell culture medium are close to each other and to the LCST of PDEGMA brushes (32 °C) . In the absence of proteins, the SPR minimum angle shifted monotonically as a function of temperature (Figure S3, Supporting Information).…”

“…Poly(di(ethylene glycol)methyl ether methacrylate) (PDEGMA) possesses a bulk LCST of 26 °C, which is increased in brushes to 32 °C, is known to afford cell and protein resistant coatings. [10,20,[28][29][30][31][32][33] In 2013, Dworak et al reported on the attachment and detachment of human fibroblasts on grafted poly(tri(ethylene glycol) ethyl ether methacrylate) brushes. [32] The polymer was reported to possess cloud points of 20 °C in cell culture medium and 24 °C in water, respectively.…”

Probing polydopamine adhesion to protein and polymer films: microscopic and spectroscopic evaluation

“…The water contact angle for PCL was higher than recorded by other groups-93.1 ± 2.5°compared to 74° [57] or 82.7 ± 3.2° [58]-as was the water contact angle for PHEMA-52.7 ± 1.9°compared to * 20° [ 59]-though the PLLA water contact angle was in agreement with other recorded values-94.8 ± 7.3°c ompared with 98.0 ± 2.3° [60]. The difference may be due to topographical differences since the dimpled textures (Fig.…”

PNIPAM grafted surfaces through ATRP and RAFT polymerization: Chemistry and bioadhesion

“…[24]. Quartz microbalance with dissipation monitoring (QCM-D) is useful to obtain the swelling behavior of polymer brushes [97].…”