Thermo-responsive stick-slip behavior of advancing water contact angle on the surfaces of poly(N-isopropylacrylamide)-grafted polypropylene membranes

Abstract

Wettability of a solid surface is highly important to its practical application, especially for the surface that shows thermoresponsive properties. In this paper, we describe a thermo-responsive stick-slip behavior of water droplets on the surfaces of poly(N-isopropylacrylamide) (PNIPAM)-grafted polypropylene membranes. Field emission scanning electron microscope (FESEM) images elucidate that the morphology of PNIPAM-grafted membrane surface is thermo-responsive, i.e., the surface becomes rougher above the lower critical solution temperature (LCST) of PNIPAM. On the surface of nascent polypropylene membranes, the water droplet shows a smooth motion resulting in advancing and receding water contact angles of 111° and ~65°, respectively. On the PNIPAM-grafted membrane surfaces, the water droplet shows a stick-slip pattern above the LCST, whereas it advances smoothly below the LCST. This phenomenon is reproducible and can be ascribed to the energy barriers enhanced by the shrink of PNIPAM chains above the LCST. We also find that the slip contact angle decreases from 102° to 92° after several stick-slip cycles. This decrease is attributed to the water adsorption on the grafted PNIPAM layer, which is confirmed by the continuous decrease of the receding water contact angle. stick-slip behavior, water contact angle, thermo-responsive surface, poly(N-isopropylacrylamide), polypropylene membrane

Deprojected analysis of Abell 1835 observed withChandraand compared withXMM-Newton

“…Applying a combined direct demodulation and deprojection technique to subtract the effects of PSF, Wang et al (2010) found that the central electron density increases by 30%, while the temperature profile is similar to the result using only a deprojection method. They also estimated that the effects of PSF were not important for the temperature profile.…”

“…After deprojection and PSF correction (Wang et al 2010), the temperature and total mass of Abell 1835 resulting from Chandra are still different from those of XMM-Newton. These differences may result from the calibration of the two instruments.…”

“…The temperature difference between the Chandra and XMM-Newton analysis also exists in Abell 1835: ∼12 keV from Chandra data (Schmidt et al 2001) and ∼7.6 keV from XMM-Newton data (Jia et al 2004). After the point-spread function (PSF) correction of XMM-Newton data, Wang et al (2010) derived a temperature profile similar to that of Jia et al (2004). Therefore, the difference is not due to the PSF effect.…”

Surface immobilization of thermo-responsive poly(N-isopropylacrylamide) by simple entrapment in a 3-aminopropyltriethoxysilane network

“…As a result, the measured Δθ A for the different ratio films, after rinsing by cold water, were ≥ 90° at 40°C. It is important to note that in literature [11, 28], contact angles on pNIPAAm brushes and coated films were reported to have discrepancy. More importantly, pNIPAAm films exhibited a stick-slip behavior above the LCST where water contact angles reached to a value as high as 111° [28] and reduced to 92° after few stick-slip cycles.…”

Nanostructured Biointerfaces: Nanoarchitectonics of Thermoresponsive Polymer Brushes Impact Protein Adsorption and Cell Adhesion

“…34 This phenomenon has been explained by the theory of a "two-component system," which basically implicates a molecular-thermal inhomogeneity in the brush structure. 35 According to the theory, the temperature differences between the very top and the bottom of the brush layer might cause certain changes in motility of polymeric chains, as well as in the dynamics of water and vapor penetration inside the brush.…”