M. Brugnara

Numerical models for the evaluation of the contact angle from axisymmetric drop profiles: A statistical comparison

Axisymmetric drop shape analysis (ADSA) is a well-established methodology for estimating the contact angle value and the surface tension of liquids starting from sessile drops images. It consists of an iterative procedure in which a best fit between a theoretical axisymmetric Laplacian curve and an experimental drop profile is performed. When only an evaluation of the geometric contact angle value is needed, a similar numerical approach can be adopted by using simpler algebraic models in place of a Laplace profile, thus allowing more straightforward implementations and shorter computation times. In this work the relative merits of the different methodologies are compared. Beside the standard ADSA procedure, four different mathematical models are examined, namely the circular and elliptical models, the first-order perturbative solution of the Laplace equation, and a cubic spline model. Their relative statistical performances are tested on both calculated and experimental drop profiles. For simulated drops, the actual capability of the models to predict the correct contact angle is also investigated.

Partially fluorinated acrylic copolymers as coatings for stone protection: characterization and surface properties

In the last decades the conservation and protection of historical buildings, after theincreased atmospheric pollution, became a priority in all industrial countries. The natural stones exposed to a dramatically increased aggressive environment show their durability limits. The necessity to study new protective systems specifically projected to defend the materials according to the peculiar characteristics of each stone substrate. The complex heterogeneity of stone substrates demands an adaptable and efficient shielding strategy in order to satisfy the different protection requirements such as water repellency, permeability, photochemical and thermal stability and transparency. These characteristics, obviously, have to be maintained as long as possible. Such modulated multi-response behaviors can only be attempted with materials based on multifunctional copolymers. Different polymeric materials have been employed as coatings for building materials but these products were always transferred from industrial applications to the conservation of Cultural Heritage without a deep knowledge of their properties and without a real optimization of structures for stone protection.

Wettability of Porous Materials III: Is the Wilhelmy Method Useful for Fabrics Analysis?

Woven and nonwoven fabrics and the corresponding fibers have been analyzed using a Wilhelmy microbalance. A self-developed analysis software (written using Labview flow-data language) has been used to extract the advancing and receding angles and also other informations commonly neglected by the standard data analysis of Wilhelmy technique, such as the immersion cross-sectional area, the effective wet perimeter, the liquid absorption, the parallelism of the straight lines describing the immersion and the withdrawal of the sample in a typical force vs immersion graph. This approach has previously been proposed for rigid porous materials such as stones and wood with some success. In the present cases some modifications of the approach have been introduced to take into account the specificity of the materials. The results appear promising for the more rigid nonwoven fabric, but suffer from a greater uncertainty and from even unacceptable inconsistencies in the case of the softer and traditional fabric. Through the application of the proposed method and software to the Wilhelmy approach the precision of the measurements can be increased in the most common cases and may help in estimating wettability. This remains true even for soft fabrics, although in this case some very important limitations of the experiment and of the model are unable to eliminate systematic errors, with the consequence that only a qualitative estimate of contact angles can be achieved.

Thermal and mechanical behavior of innovative melt-blown fabrics based on polyamide nanocomposites

A commercial organo-modified clay (OMC) was added to a polyamide 6 (PA6) matrix at various concentrations during the polymerization stage or by melt compounding in a twin-screw extruder, and the resulting pellets were used for the production of depth filters in the shape of cylindrical nonwoven webs through a melt-blown process. The processability of the investigated materials was significantly affected by nanofiller introduction. Differential scanning calorimetry revealed that OMCs play a nucleating effect on the crystallization of the polyamide matrix, with a remarkable increase in the crystallization temperature on cooling from the melt. Consequently, a parameter related to the filtering performances of the web, such as the pressure drop (ΔP) evaluated on cylindrical filters, decreased with the increase in die-to-collector distance in a more pronounced way for nanocomposite nonwovens. This behavior was related to the significant decrease of the connecting points in the networks due to the rapid cooling of the filaments on the collecting mandrel. Compressive mechanical tests evidenced how organoclay addition led to a remarkable increase of the rigidity of the web, when the data were compared at the same ΔP value, irrespectively from the preparation technique.