Ethyl p-(dimethylamino)cinnamate (EDAC) has been
used as a fluorescence probe for monitoring the
interaction
between a model water-soluble protein, bovine serum albumin (BSA), and
an anionic surfactant, sodium
dodecyl sulfate (SDS). The probe EDAC undergoes intramolecular
charge transfer (ICT) in the excited state
in water and other polar solvents. The emission from the ICT state
becomes more intense and blue-shifted
due to reduced polarity in the hydrophobic environments of BSA and SDS
micelles relative to that in pure
water. The intensity of the ICT emission from EDAC increases with
surfactant concentration and reaches a
maximum at the critical micelle concentration of SDS, which can be
employed as a simple technique for
following micellization. Analysis of the fluorescence spectra of
the probe provide evidences in favor of
surfactant-induced protein uncoiling due to massive binding of the SDS
molecules to BSA in the cooperative
binding region of the binding curve, describing protein
(BSA)−surfactant (SDS) interaction. The polarity of
the BSA−SDS aggregate formed is intermediate between that of
hydrophobic regions of BSA and SDS micelles
as sensed by the intramolecular charge-transfer (ICT) probe,
EDAC.
Successful realization of various BioMEMS devices demands effective surface modification techniques of PDMS elastomer. This paper presents a detailed report on a simple and cost effective approach for surface modification of PDMS films involving wet chemical treatment in two-step processes: primarily involving piranha solution followed by KOH dip to improve hydrophilicity and stability of PDMS surface. Chemical composition of the solution and surface treatment condition have been varied and optimized to significantly increase the surface energy. The effect of surface modification of the elastomer after wet chemical treatment is analyzed using contact angle measurement and FTIR-ATR study. PDMS surface treated in piranha solution with H 2 O 2 and H 2 SO 4 in the ratio of 2 : 3 followed by a dip in KOH solution for 15 min duration each, demonstrated a maximum reduction of contact angle to ∼27• as compared to untreated sample having a contact angle of ∼110• . The removal of hydrophobic methyl group from elastomer surface and subsequent hydrophilization of surface by wet chemical process was confirmed from FTIR-ATR spectra. This result is also supported by improved adhesion and electrical continuity of deposited aluminum metal film over the modified PDMS surface.
CdS nanocomposites have been grown in a polymer (polyvinyl alcohol) matrix using a simple chemical bath deposition process. Transmission electron micrographs of nanocomposites grown at different solution temperatures revealed the formation of isolated as well as junctionlike structures. X-ray and selected area electron diffraction patterns show that the nanocomposites are polycrystalline with cubic CdS phase. Optical band gaps of nanocomposite films are found to decrease (3.26–2.86eV) with the increase in bath temperature from 70to90°C. Photoluminescence spectra show strong green emission attributed to the Cd2+ or Cd+ ion-related recombination via moderately deep trap states. The nanocomposites show an enormous enhancement of dielectric constant in polyvinyl alcohol matrix over a frequency range of 40Hz–10MHz.
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