Search for: All records

Photocatalytic self-cleaning coatings with a high surface area are important for a wide range of applications, including optical coatings, solar panels, mirrors, etc. Here, we designed a highly porous TiO2 coating with photoinduced self-cleaning characteristics and very high hydrophilicity. This was achieved using the swelling-assisted sequential infiltration synthesis (SIS) of a block copolymer (BCP) template, which was followed by polymer removal via oxidative thermal annealing. The quartz crystal microbalance (QCM) was employed to optimize the infiltration process by estimating the mass of material infiltrated into the polymer template as a function of the number of SIS cycles. This adopted swelling-assisted SIS approach resulted in a smooth uniform TiO2 film with an interconnected network of pores. The synthesized film exhibited good crystallinity in the anatase phase. The resulting nanoporous TiO2 coatings were tested for their functional characteristics. Exposure to UV irradiation for 1 h induced an improvement in the hydrophilicity of coatings with wetting angle reducing to unmeasurable values upon contact with water droplets. Furthermore, their self-cleaning characteristics were tested by measuring the photocatalytic degradation of methylene blue (MB). The synthesized porous TiO2 nanostructures displayed promising photocatalytic activity, demonstrating the degradation of approximately 92% of MB after 180 min under ultraviolet (UV) light irradiation. Thus, the level of performance was comparable to the photoactivity of commercial anatase TiO2 nanoparticles of the same quantity. Our results highlight a new robust approach for designing hydrophilic self-cleaning coatings with controlled porosity and composition.

 

The conformal nanoporous inorganic coatings with accessible pores that are stable under applied thermal and mechanical stresses represent an important class of materials used in the design of sensors, optical coatings, and biomedical systems. Here, we synthesize porous AlOx and ZnO coatings by the sequential infiltration synthesis (SIS) of two types of polymers that enable the design of porous conformal coatings—polymers of intrinsic microporosity (PIM) and block co-polymer (BCP) templates. Using quartz crystal microbalance (QCM), we show that alumina precursors infiltrate both polymer templates four times more efficiently than zinc oxide precursors. Using the quartz crystal microbalance (QCM) technique, we provide a comprehensive study on the room temperature accessibility to water and ethanol of pores in block copolymers (BCPs) and porous polymer templates using polystyrene-block-poly-4-vinyl pyridine (PS75-b-P4VP25) and polymers of intrinsic microporosity (PIM-1), polymer templates modified by swelling, and porous inorganic coatings such as AlOx and ZnO synthesized by SIS using such templates. Importantly, we demonstrate that no structural damage occurs in inorganic nanoporous AlOx and ZnO coatings synthesized via infiltration of the polymer templates during the water freezing/melting cycling tests, suggesting excellent mechanical stability of the coatings, even though the hardness of the inorganic nanoporous coating is affected by the polymer and precursor selections. We show that the hardness of the coatings is further improved by their annealing at 900 °C for 1 h, though for all the cases except ZnO obtained using the BCP template, this annealing has a negligible effect on the porosity of the material, as is confirmed by the consistency in the optical characteristics. These findings unravel new potential for the materials being used across various environment and temperature conditions.

 

Introduction The mechanical vulnerability of the atherosclerotic cap is a crucial risk factor in asymptomatic fibroatheromas. Our research group demonstrated using numerical modeling that microcalcifications (µCalcs) located in the fibrous cap can multiply the tissue background stress by a factor 2-7[1-3]. We showed how this effect depends on the size and the ratio of the gap between particles pairs (h) and their diameter (D) along the tensile axis. In this context, we studied the impact of micro-beads of varying diameters and concentration on the rupture of human fibroatheroma laboratory models. Methods We created silicone-based (DowsilEE-3200, Dow Corning) dumbbell-shaped models (80%-scaled ASTM D412-C) of arterial tissues. Samples were divided into three groups: (1) without μBeads (control, n=12), (2) with μBeads of varying diameter (D=30,50,100μm) at a constant concentration of 1% weight (n=36), (3) with μBeads of constant diameter (D=50μm) at different concentrations (3% and 5% weight) (n=24). Before testing, samples were scanned under Micro-CT, at a resolution of 4µm. Images were then reconstructed in NRecon (SkySCan, v.2014) and structural parameters obtained in CTan (SkyScan, v.2014). These data were used to calculate the number of beads and their respective h/D ratio in a custom-made MATLAB script. We tested the samples using a custom-made micro material testing system equipped with real-time control and acquisition software (LabVIEW, v. 2018, NI). The reaction force and displacement were measured by the system and images of the sample were recorded by a high-resolution camera. The true stress and strain profiles of each sample were obtained by means of Digital Image Correlation (DIC). Results Samples with and without μBeads exhibited a distinct hyperelastic behaviour typical of arterial tissues (Fig1). Comparison of the mean ultimate stress (UTS) between groups was performed by one-way ANOVA test followed by post-hoc pairwise comparison. Regardless of the group, the presence of μBeads determined a statistically significant reduction in UTS (Fig2). Increasing the μBeads concentration was also positively correlated with lower stresses at rupture as more clusters formed resulting in lower values of h/D (Table1). Discussions Our results clearly capture the influence of μBeads on the rupture threshold of a vascular tissue mimicking material. In fact, samples with μBeads exhibit levels of UTS that are around two times lower than the control group. This effect appears to be dependent on the μBeads proximity, as lower h/D correlates with higher UTS reductions. On the other hand, the effect of particle size is not apparent for the diameters considered in this study. The plausible explanation for the observed change in rupture threshold is the increase in stress concentration around spherical μBeads, which we have previously shown in analytical and numerical studies [1-3]. Our experimental observations support our previous studies suggesting that μCalcs located within the fibroatheroma cap may be responsible for significantly increasing the risk of cap rupture that precedes myocardial infarction and sudden death.