In 2003, the most effective but simple way was proposed to synthesize double network gels, whose compression fracture stress reached about 30MPa, while that of common gels were several tens kPa. Our group has focused on PAMPSPDMAAm DN gel, because it possibly has both biocompatibility and permeability, which are good for developing artificial articular cartilage and artificial blood vessel. It is also possibly used for rapid additive manufacturing with 3D gel printer. Here, we develop a novel apparatus of the ball on disk method to observe the surface friction of the DN gels. We hope to apply this apparatus for various studies about the tribological behavior of the gels, especially about the effect of external electric field on the gel friction.
Several synthesis methods have been devised to improve the mechanical strength of gels extraordinarily after 2001. It was a trigger to use gels as a new industrial materials, since gels had been considered difficult for industrial materials because of their weakness. In a recent study, we had designed transparency shape memory gels for the first time. Shape memory gels are one of the gels with characteristic networks, and have a shape memory function by copolymerizing an acrylic monomer with a hydrophobic long alkyl side group. It is well known that the mechanical properties such as Young’s modulus and friction coefficient of shape memory gels depend on temperature. In this study, we tried to change the frictional properties of shape memory gels by laser surface texturing. Two types of processed surface were prepared. The hexagonal close packed pattern and the square close packed pattern of dimples were formed on the surface of gel sheets with CO2 laser. The intensity of laser was optimized to avoid cutting gels. The friction coefficients of unprocessed gels and two types of processed gels were measured by ball-on-disk method. Measurement partner material was sodalime glass ball. The measurement results of processed gels showed clear differences from unprocessed gels. The friction coefficients of processed gels were larger than unprocessed gels. However, these results specifically showed the velocity dependence. It indicates that surface texturing enable to control the friction coefficient of polymer gels by surface pattern and velocity.
The frictional behavior of the four kinds of high functional gels, which are double network (DN) gels, particle-double network gels (P-DN), shape memory gels (SMG), LA-shape memory gels (LA-SMG) and was studied. The velocity dependence looks similar for both the DN gels and the SMG, however the details of the dependence are different. The coefficient of the DN gels is smaller than that of the SMGs. The coefficient decreases as the normal force increases. This normal force dependence was observed for the DN gels previously, however for the first time for the SMGs. The velocity dependence looks similar for both the DN gels and the SMG, however the details of the dependence are different. The coefficient of the DN gels is smaller than that of the SMGs. The difference of the dependences is possibly related to the different softness by the temperature change of the gels. The temperature dependence of the coefficient of friction in LA-SMG was observed. Increase of the perpendicular load and the surface softness were influenced by coefficient of friction increase. In addition, the frictional coefficient of P-DN that different particle size was measured for the first time. The difference of the friction behavior of LA-SMG by the particle size was clear. Therefore, we show frictional coefficient of various high functional gels.
Gels are soft and wet materials that differ from hard and dry materials like metals, plastics and ceramics. These have some unique characteristic such as low frictional properties, high water content and materials permeability. A decade earlier, DN gels having a mechanical strength of 30MPa of the maximum breaking stress in compression was developed and it is a prospective material as the biomaterial of the human body. Indeed it frictional coefficient and mechanical strength are comparable to our cartilages. In this study, we focus on the dynamic frictional interface of hydrogels and aim to develop a new apparatus with a polarization microscope for observation. The dynamical interface is observed by the friction of gel and glass with hudroxypropylcellulose (HPC) polymer solution sandwiching. At the beginning, we rubbed hydrogel and glass with HPC solution sandwiching on stage of polarization microscope. Second step, we designed a new system which combined microscope with friction measuring machine. The comparison between direct observation with this instrument and measurement of friction coefficient will become a foothold to elucidate distinctive frictional phenomena that can be seen in soft and wet materials.
In the human body, full of biological non-Newtonian fluids exist. For example, synovial fluids exist in our joints,
which contain full of biopolymers, such as hyaluronan and mucin. It is thought that these polymers play critical roles on
the smooth motion of the joint. Indeed, luck of biopolymers in synovial fluid cause joint pain. Here we study the effects
of polymer in thin liquid layer by using an original experimental method called Film Interference Flow Imaging (FIFI). A
vertically flowing soap film containing polymers is made as two-dimensional flow to observe turbulence. The thickness
of water layer is about 4 μm sandwiched between surfactant mono-layers. The interference pattern of the soap film is
linearly related to the flow velocity in the water layer through the change in the thickness of the film. Thus the flow
velocity is possibly analyzed by the single image analysis of the interference pattern, that is, FIFI. The grid turbulence
was made in the flowing soap films containing the long flexible polymer polyethyleneoxide (PEO, Mw=3.5x106), and
rigid polymer hydroxypropyl cellulose (HPC, Mw > 1.0 x106). The decaying process of the turbulence is affected by PEO
and HPC at several concentrations. The effects of PEO are sharply seen even at low concentrations, while the effects of
HPC are gradually occurred at much higher concentration compared to the PEO. It is assumed that such a difference
between PEO and HPC is due to the polymer stretching or polymer orientation under turbulence, which is observed and
analyzed by FIFI. We believe the FIFI will be applied in the future to examine biological fluids such as synovial fluids
quickly and quantitatively.