Sensitivity of surface free energy analysis methods to the contact angle changes attributed to the thickness effect in thin films

Experimental Study of the Influence of the Adsorbate Layer Composition on the Wetting of Different Substrates with Water

Wetting is strongly influenced by adsorbate layers, which are omnipresent on surfaces. The influence of the composition and thickness of adsorbate layers on the water contact angle of sessile drops on different substrates was systematically investigated in the present work. Measurements were carried out for gold-sputtered substrates. These new results are compared to results from a previous study, in which corresponding measurements were carried out for technical steel and titanium substrates. In all experiments, different pretreatments of the samples were used to obtain variations of the adsorbate layer. The samples were either exposed to an oil bath or not, and different cleaning agents were used. The analysis of the adsorbate layer was carried out with X-ray photoelectron spectroscopy (XPS). The results for the different substrates reveal that the water contact angle depends mainly on the composition of the adsorbate layer. The substrate has only an indirect influence, as it influences the composition of the adsorbate layer. The thickness of the adsorbate layers was between 1.4 and 14 nm and was large enough to prevent a direct influence of the substrate on the water contact angle. It is shown that using the information on the adsorbate layer composition from XPS and the results for the water contact angle obtained for the gold samples alone, the water contact angles on the steel and titanium samples can be predicted.

Inverse gas chromatography in the examination of adhesion between tooth hard tissues and restorative dental materials

The adhesion is a crucial issue in the bonding of dental restorative materials to tooth hard tissues. A strong and durable bond between artificial and natural materials is responsible for the success of the restoration in the oral cavity; therefore it has to be thoroughly examined before new restorative material is introduced to the market and used clinically. Among all methods used to examine bonding strength, most of them require a large number of healthy teeth to be conducted. In this paper, the bond strength between tooth hard tissues (dentin and enamel) and an exemplary restorative composite was examined with the non-conventional method, i.e. inverse gas chromatography. Dentin and enamel from bovine teeth were separated and subjected to the standard preparation procedure using the 3-component etch-and-rinse commercial bonding system. Tissues, as well as commercial restorative composite, were examined using inverse gas chromatography. The work of adhesion between dentin/enamel and composite was calculated. Obtained results were compared with the values of shear bond strength of six configurations, i.e. etched dentin/enamel-composite, primed dentin/enamel-composite, and bonded dentin/enamel-composite. All obtained results proved that there is a correlation between the values describing bond strength obtained from inverse gas chromatography and direct mechanical tests (shear bond strength tests). It proves that inverse gas chromatography is a powerful perspective tool for the examination of bond strength between tooth hard tissues and potential dental materials without using a large number of health tooth tissues.

Inverse Gas Chromatographic Examination of Polymer Composites

Inverse gas chromatographic characterization of resins and resin based abrasive materials, polymerpolymer and polymer-filler systems, as well as dental restoratives is reviewed.

Surface characteristics of chitin-based shape memory polyurethane elastomers

Shape memory polyurethanes (SMPUs) were prepared from polycaprolactone diol 4000 (PCL 4000), 1,4-butanediol (BDO), chitin, dimethylol propionic acid (DMPA), triethylamine (TEA) and 4,4'-diphenylmethane diisocyanate (MDI), and the structures of the synthesized materials were verified by infrared spectroscopy. The effects of chitin and DMPA contents in the polyurethane formulation on surface properties were investigated. DMPA provides function of making hydrophilic polyurethanes. The crystalline structure of chitin enhanced the hydrophobicity of the synthesized materials. Contact angle, water absorption, surface free energy, work of water adhesion and swelling behavior of the synthesized polyurethanes were affected by varying the DMPA and chitin contents. The interactions of the PU films with solvents on the surface were clearly related to the contents of DMPA and chitin in the final polyurethane formulation.

Replica molding of high-aspect-ratio hydrogel pillar arrays and their stability in air and solvents

High aspect-ratio hydrogel pillars are attractive in applications, such as tissue engineering, actuation, and sensing. By replica molding from respective partially polymerized precursor solutions, followed by photocross-linking with ethylene glycol dimethacrylate (EGDMA), we successfully fabricated three kinds of high-aspect-ratio (up to 12) hydrogel pillar arrays, including poly(hydroxyethyl methacrylate) (PHEMA)-based, poly(hydroxyethyl methacrylate-co-N-isopropylacrylamide) (PHEMA-co-PNIPA)-based, and poly(ethylene glycol dimethacrylate) (PEGDMA) systems. In the dry state, all hydrogel pillars were mechanically robust and maintained their structural integrity. When exposed to water, PHEMA-co-PNIPA conical pillar array was wetted and swollen by water, which drastically decreased its Young's modulus. The combination of reduction in stiffness and capillary force between pillars caused PHEMA-co-PNIPA conical pillars to collapse on the substrate after drying from water in air. In comparison, highly cross-linked PEGDMA conical pillars were not wetted by water and maintained high stability since their Young's modulus exceeded the critical modulus required for pattern collapse by capillary force. When exposed to a lower surface energy solvent, ethanol, however, the PEGDMA conical pillars surface became wettable and the pillars collapsed after drying due to capillary force. Depending on the pillar array geometry, PEGDMA pillars dried from ethanol collapsed either randomly in the case of conical pillar array or in groups of four in the case of more densely packed circular pillars.