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A novel method was developed to detect the glass transition of thin and ultrathin polystyrene (PS) films by correlating the relationships between the temperature-dependent viscoelasticity of the PS films and stick–slip behavior on their surfaces during dynamic wetting of glycerol or oligo-poly(ethylene glycol) droplets. The peak temperature (T jm) obtained from the jumping angle–film temperature curve, in which the jumping angle Δθ was employed to scale the stick–slip behavior, was nearly identical to the corresponding T g (or T α) of the PS film. This was confirmed by dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). The change of the measured T jm with film thickness and substrate chemistry (SiO2–Si and H–Si) further confirmed that the developed method is very sensitive for detecting the dynamics of ultrathin polymer films.

The surface structures of poly(vinyl alcohol) (PVA) films with four different degrees of hydrolysis after immersion in ethanol were investigated using sum frequency generation (SFG) vibrational spectroscopy and contact angle (CA) goniometry. The result showed that the surface chemical structure of the PVA films was strongly dependent on the degree of hydrolysis. The vinyl acetate (VAc) units in the PVA chains resulting from incomplete hydrolysis segregate to the film surface and strongly affect the adsorption behavior of ethanol molecules on their surfaces. The surface hydrophilicity decreased greatly for PVA films with relatively high hydrolysis degrees (i.e., 99% and 97.7%), in which the water contact angle increased by 20°, and increased for PVA with relatively low hydrolysis degrees (95.1% and 84%) after immersion in ethanol. It was found that ethanol molecules adsorb from solution onto a PVA film surface in an ordered and cooperative way governed by hydrogen bonding when the hydrolysis degrees of PVA were higher than 98%. When the hydrolysis degree of PVA was lower than 96%, the surface structure obtained by surface reconstruction dominated after immersion in ethanol, with fewer ethanol molecules adsorbed on the surface, resulting in a decrease of its water contact angle.

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The effect of chain constraint on the surface dynamic of poly(methyl methacrylate) (PMMA) was investigated in the context of polymer tethering to a micelle core. Film surfaces dominated by either poly(methyl methacrylate) (PMMA) tethered by a poly(2-perfluorooctylethyl methacrylate) (PFMA) micelle core or non-micellized free PMMA chains are fabricated by spin coating a solution of PMMA end-capped with various numbers of FMA units onto silica substrates. By measuring the surface rearrangement kinetics of these films under thermal annealing, the onset temperature of rearrangement (T onset R ) and the activation barrier for relaxation (E a ) of surface PMMA chains are determined. It is found that the T onset R and E a of the PMMA micellized chains are 83 C and 317 kJ mol À1 , respectively, which are higher than those of the non-micellized PMMA free chains (70 C and 164 kJ mol À1 ). The T onset R and E a of PMMA in the corona increase linearly with increasing compactness of the PFMA core. The higher T onset R and E a values demonstrate the reduced mobility of surface PMMA segments tethered to a micelle core. The constraint of conformational freedom, reduction of free volume and increment of chain packing density are proposed as the speculative origins for this depressed dynamic of poly(methyl methacrylate) chains in the corona of collapsed dry micelles tethered by fluorinated block core.

The tumor-related myeloid derived suppressor cells (MDSCs), important immunosuppressive cells in tumor microenvironment, play an important role in the cancer progression. This study is aimed to investigate the crosstalk between MDSCs and oral squamous cell carcinoma (OSCC) cells and their role in the malignant progression of OSCC.

The size and shape of free volume (FV) holes available in membrane materials control the rate of gas diffusion and its permeability. Based on this principle, a segmented, thermo-sensitive polyurethane (TSPU) membrane with functional gate, i.e., the ability to sense and respond to external thermo-stimuli, was synthesized. This smart membrane exhibited close-open characteristics to the size of the FV hole and water vapor permeation and thus can be used as smart food packaging materials. Differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), positron annihilation lifetimes (PAL) and water vapor permeability (WVP) were used to evaluate how the morphological structure of TSPU and the temperature influence the FV holes size. In DSC and DMA studies, TSPU with a crystalline transition reversible phase showed an obvious phase-separated structure and a phase transition temperature at 53 o C (defined as the switch temperature and used as a functional gate). Moreover, the switch temperature (T s ) and the thermal-sensitivity of TSPU remained available after two or three thermal cyclic processes. The PAL study indicated that the FV hole size of TSPU is closely related to the T ·d, which produced an "increase-decrease" response to the thermo-stimuli. This phase transition accompanying significant changes in the FV hole size and WVP can be used to develop "smart materials" with functional gates and controllable water vapor permeation, which support the possible applications of TSPU for food packaging.