Atomic Force Microscopy Phase Contrast Research Articles

Surface modification of maize starch films by low-pressure glow 1-butene plasma

Plasma polymerisation was used to modify the surface of maize starch films in order to reduce their water affinity. Films were prepared by casting starch suspensions heated for different periods of time. Glycerol was added as a plasticiser. To produce a hydrogenated-carbon coating, films were exposed to low-pressure glow plasma generated in 1-butene gas from a radio frequency diode sputtering system. Atomic force microscopy (AFM) was used to investigate possible changes in surface morphology and roughness of plasma-coated films in relation to the corresponding substrates. AFM phase contrast images at high magnification revealed characteristic features at the surfaces of plasma-coated starch films. Water absorption experiments and contact angle measurements were carried out to verify the effect of deposited layers on the water sensitivity of those surface-modified films. The results indicated that the coating process reduced significantly the hydrophilic character of starch films.

Effect of aging on the microstructure of plasticized cornstarch films

Aging of cornstarch films prepared by casting was investigated. Water and glycerol-plasticized cornstarch films were stored at 50% relative humidity over a period of 330 days. Aging was followed by X-ray diffraction (XRD) and atomic force microscopy (AFM). XRD spectra indicated development of B-type crystallinity even for fresh films and that the crystallinity index increased from 0.06 to 0.28 as a function of storage time. AFM images of 270-day-old films revealed that the general morphology and the overall roughness have not changed due to aging. AFM phase contrast images at higher magnification showed an increasing number of ordered domains at the surface of these films, which may be attributed to recrystallization of amylose. No morphological change was observed at least at the surface of the granular region, which is enriched in amylopectin.

Poly(ethylene oxide)/Silica Nanocomposites: Structure and Rheology

The effects of polymer−particle and particle−particle interactions on viscoelastic properties of nanocomposite materials are investigated using narrow molecular weight distribution poly(ethylene oxide) (PEO) containing isotropic silica nanospheres. Nanocomposites are prepared using a “freeze-drying” method to guarantee homogeneous dispersion of silica. The dispersion state of silica nanospheres is characterized by atomic force microscopy phase contrast imaging, and mechanical rheometry is used to study relaxation dynamics and viscoelastic properties of these materials in the melt state. Linear viscoelastic data indicate a transition to a solidlike response at low oscillation frequencies for particle volume fractions φ as low as 2%, dramatically lower than the theoretical percolation threshold (φ ∼ 30%). Nanoparticle volume fraction, surface chemistry, and PEO molecular weight are all found to strongly influence nanocomposite structure and dynamics. A filler networking mechanism, wherein nanosized silica p...