A hydrophobic to hydrophilic gradient surface was prepared using the tuned photodegradation of an alkylsilane self-assembled monolayer (SAM) using irradiation of vacuum ultraviolet light (wavelength=172 nm). The water contact angle on the photodegraded SAM surface was adjusted using the intensity and time photoirradiation parameters. The formation of a gradient was confirmed by fluorescent labeling. The water drop moved from the hydrophobic to hydrophilic surface with a velocity that depended on the gradient. The higher the gradient, the faster the water moved. For the first time, we have prepared a gradient surface using photodegradation where the movement of a water drop was regulated by the degree of gradation. Considering that the photodegradation technique can be applied to various surfaces and to lithography, this technique will be useful for various material surfaces.
Small-angle scattering of soft X-rays by polystyrene latex spheres was studied using the synchrotron radiation from the electron synchrotron operated at about 1 GeV at the Institute for Nuclear Study, University of Tokyo. The exposure time required to make three smallest-angle diffraction peaks visible on a photographic plate was 2 min with the soft X-rays (46.8 Å) of the synchrotron radiation, compared to 400 min with the CKα radiation (44.8 Å) from the X-ray tube operated at 3 kV ×50 mA. The diffraction patterns were so distinct that inter-particle interference functions could be derived with four diffraction peaks. Experimental results as a whole suggest that soft X-rays in the synchrotron radiation will be very useful in studying two-dimensional structures of thin organic materials with the thickness of microns or submicrons.
The swelling behavior and hierarchical structures of poly(acrylic acid) (AA) homopolymer gels and poly(12-acryloyloxydodecanoic acid (ADA)-co-AA) gels carrying ionizable groups as well as hydrophobic groups have been investigated by equilibrium swelling measurement, dynamic light scattering (DLS), and small-angle neutron scattering (SANS). The equilibrium swelling degree (Sv) and the structure factors of the copolymer gels were obtained as a function of the ethanol (EtOH)/water (W) solvent composition, x (= vol % of EtOH). Sv showed a convex-upward function of x. That is, the gels swelled with increasing x until x = 50−60 vol % for AA gels and x = 70−80 vol % for ADA/AA gels and then decreased gradually. This phenomenon is explained by hydrophobic association of long alkyl chains of ADA and a cosolvency effect of poly(AA) in EtOH and W. The DLS results also indicated that the major component of light scattering was frozen inhomogeneities. SANS intensity functions, I(q), for the copolymer gels when x = 25 vol % showed the presence of an ordered structure in water with a long spacing of ca. 46 Å. These experimental pieces of evidence suggest a strong correlation between the macroscopic properties, such as Sv, and the microscopic structure as well as the dynamics. The diffusion coefficients were obtained by DLS as well as SANS, of which physical meanings are discussed by comparing the x dependence of Sv.
