Abstract
Cellulose derivate phase separation in thin films was applied to generate patterned films with distinct surface morphology. Patterned polymer thin films are utilized in electronics, optics, and biotechnology but films based on bio-polymers are scarce. Film formation, roughness, wetting, and patterning are often investigated when it comes to characterization of the films. Frictional properties, on the other hand, have not been studied extensively. We extend the fundamental understanding of spin coated complex cellulose blend films via revealing their surface friction using Friction Force Microscopy (FFM). Two cellulose derivatives were transformed into two-phase blend films with one phase comprising trimethyl silyl cellulose (TMSC) regenerated to cellulose with hydroxyl groups exposed to the film surface. Adjusting the volume fraction of the spin coating solution resulted in variation of the surface fraction with the other, hydroxypropylcellulose stearate (HPCE) phase. The film morphology confirmed lateral and vertical separation and was translated into effective surface fraction. Phase separation as well as regeneration contributed to the surface morphology resulting in roughness variation of the blend films from 1.1 to 19.8 nm depending on the film composition. Friction analysis was successfully established, and then revealed that the friction coefficient of the films could be tuned and the blend films exhibited lowered friction force coefficient compared to the single-component films. Protein affinity of the films was investigated with bovine serum albumin (BSA) and depended mainly on the surface free energy (SFE) while no direct correlation with roughness or friction was found. BSA adsorption on film formed with 1:1 spinning solution volume ratio was an outlier and exhibited unexpected minimum in adsorption.
Highlights
Spinodal decomposition of polymer blends can generate thin films with multi-phase surface composition, and often, complex morphology (Heriot and Jones, 2005)
The friction behavior was analyzed by Friction Force Microscopy (FFM) and compared to the adhesive properties of the surfaces of the pure and blend films obtained from Atomic force microscopy (AFM) force spectroscopy
Spin coated trimethyl silyl cellulose (TMSC) and hydroxypropylcellulose stearate (HPCE) films formed into smooth one-component film morphologies—indicating a uniform film formation—while the blend films containing both derivatives resulted in films with spinodal decomposition and are presented via three composition ratios, 3:1, 1:1, and 1:3 (Figure 2A)
Summary
Spinodal decomposition of polymer blends can generate thin films with multi-phase surface composition, and often, complex morphology (Heriot and Jones, 2005). We apply spinodal separation to generate periodical cellulose blend film hierarchies and evaluate the morphology and configuration and discuss their relation to antifouling surfaces. FFM was employed to correlate friction to viscoelastic relaxation (Hammerschmidt et al, 1996; Sondhauß et al, 2015) and to characterize photoreactive organic surface patterns of spin casted thin films (Hlawacek et al, 2009; Shen et al, 2014). The friction behavior was analyzed by FFM and compared to the adhesive properties of the surfaces of the pure and blend films obtained from AFM force spectroscopy. The comprehensive information obtained by surface characterization was employed to determine the influence of adhesive and tribological surface properties of the cellulose-HPCE blend films on bovine serum albumin (BSA) adsorption investigated by surface plasmon resonance spectroscopy (SPR) and Quartz Crystal Microbalance with Dissipation monitoring (QCM-D)
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