Extruded samples of starch-casein blends were processed by using a single-screw extruder. The independent variables in the process were temperature (126-1947C), moisture content (18-29%) and starch-casein blend (5-95%). These independent variables affected significantly the physicochemical and textural properties of the biopolymers. The highest values for expansion (EXP) and water absorption index (WAI) were found when a higher starch proportion was present in the blends, at 1267C barrel temperature and moisture content higher than 25%. By increasing the barrel temperature, from 1267C to 1947C, the water solubility index (WSI) and color parameter were increased. Initial viscosity (IV) and viscosity at 907C (V90) were mainly affected by the barrel temperature at 1947C. However, the viscosity at 507C (V50) was affected neither by the different extrusion variables nor by the biopolymer proportion in the blends. Compression force (CF) was strongly dependent on moisture content and casein proportion in the blend. The higher CF values were found at starch concentrations around 50% and 25% moisture content, for higher or lower values than these the obtained extruded products were softer and consequently had lower CF values.

No abstract

The aim of this work was to synthesize silver nanoparticles (NPs) through a green synthesis method using starch as a capping agent. The influence of the glucose content, temperature, and pH on the size of the NPs was evaluated by means of a response surface methodology. The obtained nanomaterials were characterized by UV-Vis spectroscopy, XRD, and TEM, and the crystalline structure of the silver was determined by XRD. The optimum synthesis time was after 3 h of reaction time the colloidal solution, did not show any further significant variation in the optical absorption peak (l max ). Response surface results indicate that the reducing agent (glucose) concentration was the most important factor influencing the NPs size, which ranged from 2 to 24 nm. TEM images show that NPs had predominantly spherical shapes, but also polyhedral shapes were present in smaller quantities. Analysis of Raman spectra infers that the glucose initially reduces silver ions to elemental silver. Then the starch undergoes hydrolysis providing primary hydroxyl that contributes to the reduction of silver. The carboxyl and hydroxyl groups of glucose and hydrolyzed starch stabilize the silver NPs by passivating their surface, so that they do not aggregate and remain uniformly distributed.

The room temperature thermal diffusivity evolution of electrochemically formed porous silicon as a function of the etching time is investigated. The measurements were carried out using the open-cell photoacoustic technique. The experimental data were analyzed using a composite two-layer model. The results obtained strongly support the existing studies, indicating the presence of a high percentage of SiO 2 in the composition of porous silicon material. [S0031-9007(97) PACS numbers: 44.30. + v, 61.43.Gt, 81.05.Cy, 81.05.Rm Since the discovery of its room-temperature visible luminescence [1][2][3][4][5], porous silicon (PS) has become a subject of considerable interest, especially for its promising use as an optoelectronic device [6,7]. There are several methods [8][9][10][11] for fabricating PS from crystalline silicon wafers. The electrochemical etching [1,8] is, however, the most extensively used so far. The morphology of the resulting porous layer is strongly dependent upon the fabrication controlling parameters such as electrolyte composition, current density, etching time, etc., as well as on the type of substrate used.In general, an electrochemically formed n-type PS layer consists essentially of a double-layer system on top of the silicon substrate [1,12]. The outermost thin layer, known as the microporous layer, is typically 10-15 mm thick and is responsible for the observed photoluminescence. Except for very small etching times, the inner layer adjacent to the crystalline substrate, designated as the macroporous layer, consists of a parallel array of airembedded free-standing n-PS columns.Despite the large body of literature that already exists on PS [13,14], so far there has been no reported detailed investigation of the thermophysical properties of this important system. In this Letter we apply the modern photothermal techniques to the evaluation of the thermal properties of electrochemically formed n-PS.The samples used in our experiments were prepared by electrochemical etching on (100) oriented, nondegenerated, n-type ͑2.1 3 10 18 cm 23 ͒ crystalline silicon. The samples had a thickness of roughly 300 mm and an electrical resistivity of 1-5 V cm. The electrochemical etching was carried out following the procedure outlined in Ref. [12]. The crystalline samples, with an appropriate Pt network electrode attached to them, were immersed in a 150 ml Becker filled with HF. A current density of 40 mA͞cm 2 was then applied to the samples using a HP-model 6206B dc power supply operating between 5-10 V. During the etching period the samples were always kept under the irradiation of a 250 W infrared lamp positioned roughly 20 cm away from the etching bath. By controlling the etching time, ranging from 10 to 83 min, we could fabricate samples with different macroporous thicknesses.In Fig. 1 we show the side view optical micrograph of a typical n-PS sample, produced with 60 min etching time. The three distinct regions mentioned above, namely, the microporous and macroporous layers on top of the crystalline sub...

BACKGROUND: Several storage techniques have been developed to extend the post-harvest shelf life of horticultural products. One method involves the use of edible or biodegradable coatings. Such coatings are made of biological materials that are used to coat fresh products, providing a semi-permeable barrier to water vapour and gases, e.g. O 2 and CO 2 . The influence of starch concentration, glycerol content and pH on the carbon dioxide permeability (CO 2 P) and mechanical properties of gelatine-starch edible films were evaluated.

From photoacoustic (PA) experiments we determine the nonradiative carrier lifetime in direct band-gap semiconductors. We use the Rosencwaig and Gerscho model to calculate the PA signal in semiconductors taking into account the distinction between non-radiative and radiative carrier lifetimes. We have assumed that for our high quality crystalline samples, the main contribution to the non-radiative processes comes from CHCC and CHSH Auger recombination for n and p-type materials, respectively. For GaAs, InSb and GaSb samples, the experimental data obtained by means of an open photoacoustic cell were fitted to the theoretical model and we show that the values we determined for the non-radiative recombination lifetime agree well with those reported in the literature.

There were significant differences between treatments according to the analysis of variance (p ≤0.05).The different letters indicate significant differences between the Tukey means test (α = 0.05, n=9). ND: Not detected.

We present a method for determining the thermal diffusivity in opaque solids by means of an analysis of the photoacoustic phase signal at low modulation frequencies using the open-cell photoacoustic technique. We show for f ⩽ (π/2) 2 fc, where fc is the modulation frequency at which the thermal diffusion length matches the sample thickness, the photoacoustic phase signal can be written in linear form with the modulation frequency f. Then, obtaining the proportionality coefficient by fitting the experimental data, the thermal diffusivity of the sample can be determined. The advantage of this method is that it is realized in a range of modulation frequencies below those normally used, hence, the photoacoustic signal should be alone attributed to the mechanism of thermal diffusion. Moreover, the signal-to-noise ratio will be more reliable. This method was tested in some samples and it is also shown to be important in solids with high diffusivity values and thin materials.