Andreea Irina Barzic

Chain flexibility versus molecular entanglement response to rubbing deformation in designing poly(oxadiazole-naphthylimide)s as liquid crystal orientation layers

Four poly(oxadiazole-imide)s containing naphthalene rings, with different flexibility and molecular weight, are investigated with respect to their rheological properties to establish the optimal processing conditions from solution phase to film state for liquid crystal orientation purposes. The film uniformity and strength are determined by monitoring the flow behavior and chain entanglements. The solution rheological data are in agreement with film tensile testing, revealing that higher molecular weight favors chain entanglements and implicitly the film mechanical resistance. In order to analyze the suitability of these films as alignment layers their surface is patterned by rubbing with two types of velvet. Liquid crystal alignment of 4′-pentyl-4-biphenylcarbonitrile nematic is tested by polarized light microscopy. The resulting behavior is correlated with the polyimide malleability and characteristics of the textile fibers, namely their polarity, size, and mechanical features. The competitive effects between chain flexibility and entanglements, together with the interactions occurring between the polymer and velvet are analyzed in order to explain the surface regularity, which influences the uniformity of the liquid crystal alignment. The contrast between dark and bright states recorded on the liquid crystal cell indicates that some of these polynaphthalimides are promising candidates for liquid crystal display devices.

Statistical analysis on morphology development of some semialicyclic polyimides using atomic force microscopy

The morphological features and surface texture parameters of some polyimide films prepared from a flexible and alicyclic dianhydride, in combination with five aromatic diamines, were evaluated by atomic force microscopy (AFM) in order to determine their applicability in electronics. By means of the surface roughness, shape of the surface height distribution, and angular and radial texture, a precise description of the actual surface topographies at the interface with other materials was made. The polyimide structures led to the development of different surface morphologies (from granular to porous and from bumpy to spiky). The relief diversity was described by the entropy of morphology, which had a similar trend with the root mean square roughness, which presents low values, i.e. 0.5–1.8 nm. Three‐dimensional AFM images and the corresponding angular spectra, together with texture aspect ratio and texture direction index (close to 1), indicate that no predominant orientation exists on the investigated surfaces. The redundancy in the morphology was associated with the concept of fractals, the maximum redundancy being achieved for the polyimide with the most complex polymer chain conformation. These results provide useful insights in selecting the polyimide structure, which has the optimal morphology, roughness, orientation, bearing properties, or self‐similarity for microelectronic applications such as: substrate for display backplanes, planar technology, microelectronic packaging, etc. Microsc. Res. Tech. 76:503–513, 2013.

Surface topography effect on fibroblasts population on epiclon-based polyimide films

A polyimide based on alicyclic units, such as epiclon (5-(2,5-dioxotetrahydrofurfuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic acid anhydride), was investigated from the point of view of its surface features to check their suitability for cell culture applications. Atomic force microscopy data revealed fractal and isotropic surfaces with nanoscale roughness and peaks placed at much smaller distances comparing to the cell size scale, favoring a good compatibility of the synthesized material with the biological medium, particularly after plasma treatment. Surface tension properties were determined in order to evaluate the interactions at the bio-interface affecting the adherence behavior of cell-binding proteins to the sample surface. In vitro experiments regarding the cytocompatibility and population tendency reveal that polyimide allows cells to adhere and to proliferate onto the surface. These tests indicate that the studied epiclon-based polyimide is not cytotoxic and can be recommended as good candidate for cell culture substrate in tissue engineering, especially after plasma treatment.

Study on glucose release ability from hydroxypropyl cellulose films

Drug delivery systems based on different glucose and hydroxypropyl cellulose (HPC) ratios were prepared and characterized to check their suitability as controlled drug delivery carriers. The surface polarity and topography were analyzed and correlated with the glucose/HPC ratio and the drug release mechanism. Different mathematical models were used to fit the “in vitro” release data to understand the glucose release mechanism. The in vitro release data analyzed using various kinetic models showed that all the samples were governed by first-order kinetics; however, one sample seems to have a behavior closer to zero-order kinetics. When a higher percentage HPC was added, the release process was described by Fickian diffusion. An anomalous diffusion was correlated with a lower HPC content. The study showed that glucose/HPC is an interesting matrix for the preparation of controlled release systems which can provide a constant glucose dose over a 4-h period.

Optical Rotatory Dispersion of Poly(propylene oxide) in Benzene Solution Determined from Channeled Spectra

The proposed method of channeled spectrum employs the recorded channeled spectrum of an optical active polymer solution placed between two crossed polarizers. The approach allows the evaluation of the optical rotatory dispersion of poly(propylene oxide) in benzene. The specific rotation, circular birefringence, and dispersion parameter depend on the wavelengths of the maxima and minima from the channeled spectrum.

Semi-Alicyclic Polyimides: Insights into Optical Properties and Morphology Patterning Approaches for Advanced Technologies

© 2012 Barzic et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Semi-Alicyclic Polyimides: Insights into Optical Properties and Morphology Patterning Approaches for Advanced Technologies

Refraction and polarization properties of some fluorinated imidic polymers

Several new fluorinated imidic polymers were analyzed from optical and dielectric point of view. The main achievement of this work consists in the establishment of novel insights in the structure–property correlation by optimization of certain monomer features. Group contribution and Bicerano theories were utilized to calculate molar volume and molar refraction and atomic connectivity indices, respectively. These are further used to obtain the refractive index and from the latter the dielectric constant. Both macromolecular architecture and backbone polarizability affect refraction and polarization properties of specimens. The values of refractive index are reduced by using diamine residues that decrease chain packing and increase density of –CF3 groups, whereas inserting dianhydride moieties with less bulky character and smaller numbers of low polarizable groups led to the reverse result. The resulted data are important in controlling the physical performance of imidic polymers as demanded by electronic applications.

Molecular design of some semi-alicyclic polyimides as a route to improve refraction and dielectric properties for liquid crystal display applications:

The study establishes an adequate monomer combination for achieving the best balance of properties required in obtaining polyimide alignment layers for display devices. The molecular design of some aliphatic/aromatic polyimides was performed by using dianhydride monomers with distinct configurations in terms of rigidity, size, and symmetry. The polyimides based on semi-flexible and nonsymmetric dianhydride moieties present lower refractive index and dielectric constant (<3) than those obtained from symmetric and rigid dianhydride units. This determines faster traveling of visible and microwave radiations as required for liquid crystal alignment purposes. The interactions of samples with the N-(4-Methoxybenzylidene)-4-butylaniline, cyanobiphenyl, and 4-pentyl-4-cyanobiphenyl nematics were assessed. The analyzed polyimides have higher surface tensions than the ones of the liquid crystals, determining a parallel arrangement of the nematic molecules. As the dispersive interactions at the polymer surface are lower, the work of spreading is higher as a result of improved adhesion of liquid crystal with the polyimide alignment layer. The sample containing rigid, symmetric, noncoplanar dianhydride units (PI.4) and the one based on semi-flexible, nonsymmetric dianhydride moieties are the most transparent for visible and microwave radiations, allowing low cohesion interaction at interface with nematics. These aspects recommend the two studied polyimides as candidates for alignment layers.

On the Effects of UV Radiation on the Release Ability of Glucose Embedded in Hydroxypropyl Cellulose Films

ABSTRACT New drug delivery systems based on hydroxypropyl cellulose (HPC) and different percents of glucose were prepared and characterized to check their suitability as UV resistant patches. The spectral absorption properties of the HPC and HPC-glucose blends before and after UV irradiation were analyzed. The surface polarity and hydrophilicity were correlated with the morphology of the films and analyzed with respect to the UV exposure time and the embedded amount of glucose. The effects of UV radiation on in vitro evaluation of glucose release from the HPC films are reported. The mechanism involved in the drug release process, evaluated using the Korsmeyer-Peppas equation, was dependent on the introduced amount of glucose and less on the UV exposure time. A more polar, smoother, and less dense surface releases the glucose over larger periods of time, making the system with lower percents of glucose more adequate for the pursued purpose.

Polyimide surface modification by RF plasma for biocide attachment

ABSTRACT This article has been retracted.