Evaluation of the performance enhancement of silicone biofouling-release coatings by oil incorporation

In response to increased evidence of ecosystem damage by toxic antifouling paints, many researchers have developed nontoxic silicone fouling release coatings. The fouling release capability of these Systems may be improved by adding nonbonding silicone oils to the coating matrix. This idea has been tested by comparing the adhesion strength of hard- and soft-fouling organisms on a cured polydimethylsilicone (PDMS) network to that of the same network containing free polydi-methyldiphenylsilicone (PDMDPS) oil at five exposure sites in North America and Hawaii. Fouling coverage is discussed, together with the bioadhesion data, to emphasize that although these coatings foul the fouling is easily removed. The partitioning of the incorporated oil upon exposure of the coatings to a simulated marine environment containing sediment was determined. Less than 1.1 wt% of the incorporated oil was lost from the coating over one year, and the toxicity of these coatings was shown to be minimal to shrimp and fish. Brush abrasion wear was greater for coatings containing free oil, but the modulus of elasticity was not appreciably decreased by the addition of 10wt% free oil.     

Nanostructured metal coatings on polymers increase osteoblast attachment

Bioactive coatings are in high demand to increase the functions of cells for numerous medical devices. The objective of this in vitro study was to characterize osteoblast (bone-forming cell) adhesion on several potential orthopedic polymeric materials (specifically, polyetheretherketone, ultra-high molecular weight polyethylene, and polytetrafluoroethylene) coated with either titanium or gold using a novel Ionic Plasma Deposition process which creates a surface-engineered nanostructure (with features below 100 nm). Results demonstrated that compared to currently-used titanium and uncoated polymers, polymers coated with either titanium or gold using Ionic Plasma Deposition significantly increased osteoblast adhesion. Qualitative cell morphology results supported quantitative adhesion results as increased osteoblast cell spreading was observed on coated polymers compared to uncoated polymers. In this manner, this in vitro study strongly suggests that Ionic Plasma Deposition should be further studied for creating nanometer surface features on a wide variety of materials to enhance osteoblast functions necessary for orthopedic applications.     

Silicone fouling-release coatings: effects of the molecular weight of poly(dimethylsiloxane) and tetraethyl orthosilicate on the magnitude of pseudobarnacle adhesion strength

A series of poly(dimethyl siloxane) (PDMS)/silica nanocomposites were synthesized utilizing a sol gel method. The samples were evaluated using pseudobarnacle adhesion and tensile strength tests. The effects of the molecular weight of the PDMS and the size and structure of the silica domains on biofouling release and the mechanical behavior of the PDMS/silica materials were investigated. Three different molecular weights (18,000, 49,000 and 79,000 g mol(-1)) of hydroxyl-terminated PDMS (HT-PDMS) were used to prepare the nanocomposites with three different weight ratios (1:1, 3:1 and 5:1) of HT-PDMS to tetraethyl orthosilicate (TEOS). TEOS served as a crosslinker to form PDMS networks and as a precursor to form silica domains. Two different variants of TEOS with regard to its degree of polymerization (n) (monomeric type: n ≈= 1 and oligomeric type: n ≈= 5) were used for in situ formation of silica particles via the sol-gel process. The mechanical properties of the composites were characterized using stress-strain isotherms. All the mechanical properties evaluated (Young's modulus, tensile strength, energy required for rupture, elongation at break) improved with increases in the molecular weight of the HT-PDMS and the silica content. The pseudobarnacle adhesion test was used to examine the fouling- release (FR) properties of coatings applied on aluminum plates. The rupture energy and tensile strength increased substantially when oligomeric TEOS was employed in the PDMS/silica composites. Scanning electron microscopy (SEM) was used to investigate the structure of the silica domains. It was found that the use of oligomeric TEOS in higher molecular weight PDMS samples with higher PDMS/TEOS weight ratios led to low pseudobarnacle adhesion strengths of ≈ 0.3 MPa, which is in the range of commercial FR coatings.     

Mechanical aspects of silicone coatings for hard foulant control

Barnacle release mechanisms and the durability of silicone coatings have been studied. Release studies were performed on both transparent, single‐layer silicone coatings and duplex silicone coatings. The release forces of pseudobarnacles (epoxied studs) and Chesapeake Bay barnacles (Balanus improvisus) were measured with a pull‐off (tension) tester; modes of release were revealed in video recordings of the separation process from transparent coatings on glass. Scratch tests with 0.8 mm spherically‐tipped diamond provided a measure of durability (tear resistance). Release forces from both coatings decreased as coating thickness increased. Both pseudobarnacles and barnacles separated by a peeling process, although differences in peeling modes were seen. The durability of coatings increased with increasing coating thickness. Release behavior is discussed in terms of a fracture mechanic's model for pull‐off separation, and the differences in adhesion between barnacles and pseudobarnacles are described.     

Release characteristics of reattached barnacles to non-toxic silicone coatings

Release mechanisms of barnacles (Amphibalanus amphitrite or Balanus amphitrite) reattached to platinum-cured silicone coatings were studied as a function of coating thickness (210-770 microm), elastic modulus (0.08-1.3 MPa), and shear rate (2-22 microm s(-1)). It was found that the shear stress of the reattached, live barnacles necessary to remove from the silicone coatings was controlled by the combined term (E/t)(0.5) of the elastic modulus (E) and thickness (t). As the ratio of the elastic modulus to coating thickness decreased, the barnacles were more readily removed from the silicone coatings, showing a similar release behavior to pseudobarnacles (epoxy glue). The barnacle mean shear stress ranged from 0.017 to 0.055 MPa whereas the pseudobarnacle mean shear stress ranged from 0.022 to 0.095 MPa.     

Adhesion study of silicone coatings: the interaction of thickness,modulus and shear rate on adhesion force

Abstract

Interactions between coating thickness, modulus and shear rate on pseudobarnacle adhesion to a platinum-cured silicone coating were studied using a statistical experimental design. A combined design method was used for two mixture components and two process variables. The two mixture components, vinyl end-terminated polydimethylsiloxanes (V21: MW = 6 kg mole^?1 and V35: MW = 4 9.5 kg mole^?1, Gelest Inc.) were mixed at five different levels to vary the modulus. The dry coating thickness was varied from 160 – 740 μm and shear tests were performed at four different shear rates (2, 7, 12, and 22 μm s^?1). The results of the statistical analysis showed that the mixture components were significant factors on shear stress, showing an interaction with the process variable. For the soft silicone coating based on the high molecular weight polydimethylsiloxane (E = 0.08 MPa), shear stress significantly increased as coating thickness decreased, while shear rate slightly impacted shear force especially at 160 μm coating thickness. As the modulus was increased (E = 1.3 MPa), more force was required to detach the pseudobarnacle from the coatings, but thickness and rate dependence on shear stress became less important.     

Adhesion study of silicone coatings: the interaction of thickness, modulus and shear rate on adhesion force

Interactions between coating thickness, modulus and shear rate on pseudobarnacle adhesion to a platinum-cured silicone coating were studied using a statistical experimental design. A combined design method was used for two mixture components and two process variables. The two mixture components, vinyl end-terminated polydimethylsiloxanes (V21: MW=6 kg mole(-1) and V35: MW=4 9.5 kg mole(-1), Gelest Inc.) were mixed at five different levels to vary the modulus. The dry coating thickness was varied from 160 - 740 microm and shear tests were performed at four different shear rates (2, 7, 12, and 22 microm s(-1)). The results of the statistical analysis showed that the mixture components were significant factors on shear stress, showing an interaction with the process variable. For the soft silicone coating based on the high molecular weight polydimethylsiloxane (E=0.08 MPa), shear stress significantly increased as coating thickness decreased, while shear rate slightly impacted shear force especially at 160 microm coating thickness. As the modulus was increased (E=1.3 MPa), more force was required to detach the pseudobarnacle from the coatings, but thickness and rate dependence on shear stress became less important.     

The development of marine biofilms on two commercial non-biocidal coatings: a comparison between silicone and fluoropolymer technologies

The antimicrobial performance of two fouling-release coating systems, Intersleek 700? (IS700; silicone technology), Intersleek 900? (IS900; fluoropolymer technology) and a tie coat (TC, control surface) was investigated in a short term (10 days) field experiment conducted at a depth of ca 0.5 m in the Marina Bandar Rawdha (Muscat, Oman). Microfouling on coated glass slides was analyzed using epifluorescence microscopy and adenosine-5'-triphosphate (ATP) luminometry. All the coatings developed biofilms composed of heterotrophic bacteria, cyanobacteria, seven species of diatoms (2 species of Navicula, Cylindrotheca sp., Nitzschia sp., Amphora sp., Diploneis sp., and Bacillaria sp.) and algal spores (Ulva sp.). IS900 had significantly thinner biofilms with fewer diatom species, no algal spores and the least number of bacteria in comparison with IS700 and the TC. The ATP readings did not correspond to the numbers of bacteria and diatoms in the biofilms. The density of diatoms was negatively correlated with the density of the bacteria in biofilms on the IS900 coating, and, conversely, diatom density was positively correlated in biofilms on the TC. The higher antifouling efficacy of IS900 over IS700 may lead to lower roughness and thus lower fuel consumption for those vessels that utilise the IS900 fouling-release coating.     

The development of marine biofilms on two commercial non-biocidal coatings: a comparison between silicone and fluoropolymer technologies

The antimicrobial performance of two fouling-release coating systems, Intersleek 700® (IS700; silicone technology), Intersleek 900® (IS900; fluoropolymer technology) and a tie coat (TC, control surface) was investigated in a short term (10 days) field experiment conducted at a depth of ca 0.5 m in the Marina Bandar Rawdha (Muscat, Oman). Microfouling on coated glass slides was analyzed using epifluorescence microscopy and adenosine-5′-triphosphate (ATP) luminometry. All the coatings developed biofilms composed of heterotrophic bacteria, cyanobacteria, seven species of diatoms (2 species of Navicula, Cylindrotheca sp., Nitzschia sp., Amphora sp., Diploneis sp., and Bacillaria sp.) and algal spores (Ulva sp.). IS900 had significantly thinner biofilms with fewer diatom species, no algal spores and the least number of bacteria in comparison with IS700 and the TC. The ATP readings did not correspond to the numbers of bacteria and diatoms in the biofilms. The density of diatoms was negatively correlated with the density of the bacteria in biofilms on the IS900 coating, and, conversely, diatom density was positively correlated in biofilms on the TC. The higher antifouling efficacy of IS900 over IS700 may lead to lower roughness and thus lower fuel consumption for those vessels that utilise the IS900 fouling-release coating.     

Mussel attachment on rocky shores: the effect of flow on byssus production

Mussels rely on a strong byssal attachment to persist in a range of habitats with differing rates of water flow. Recent studies, however, suggest that the ability of one mussel species to sense and respond adaptively to the flow in its environment is limited under even modest flow conditions because the process of byssal thread formation is disrupted. This study extends these findings to four mussel species, Mytilus trossulus, M. galloprovincialis, M. californianus, and Modiolus modiolus. Collectively, the response of byssal thread formation decreased with rates of flow above ～25 cm/s and the critical flow threshold was estimated to be <50 cm/s. How can mussels persist on shores where flow is an order of magnitude higher? Using a combination of techniques for measuring flow, velocity profiles were obtained above and within mussel aggregations in the laboratory and in the field. Flow was greatly reduced within mussel aggregations, ranging from 0.1% to 10% of free-stream velocity. These results suggest one key to the success of mussels in habitats with high rates of flow is the ability to form aggregations that ameliorate flows to a level that is conducive to byssal thread formation.     

Childhood adversity,attachment security,and adult relationships: A preliminary study

Several evolutionary theorists have linked early rearing context to later reproductive strategy, hypothesizing that strategies differentiate during development as functional responses to ecological characteristics, by individuals or through parental manipulation. Attachment security has been proposed as a mediator. In this study, 40 young adults were given a multidimensional assessment, including the Hazen and Shaver Adult Attachment Questionnaire. Twenty-four subjects were classified as having secure attachment styles, 16 as nonsecure. The magnitude and predictability of parental investment during childhood was classified as lower if there was a brief intersibling interval, parental divorce, fewer economic resources, or less nurturing parents (i.e., more childhood adversity). Several such indicators were present for 17 people, 12 of whom were nonsecure, compared to only 4 of the 23 others. The nonsecurely attached subjects were less likely to have attained enduring marriages. The 6/16 nonsecure who had a marriage or cohabitation began them at a younger age and after a shorter courtship period than did the 15/24 secure with such relationships. Separations or divorces had already occurred in the relationships of 4/6 nonsecure versus 5/15 secure. Attachment security was associated with childhood adversity and adult relationships for both men and women, when analyzed separately. A retrospective study cannot address cause and effect, because poor adult relationship outcomes might bias recall of parental behavior. However, results are consistent with theories that unpredictable early environments foster short-term rather than long-term mating strategies, possibly through affecting attachment styles.     

涂料微生物污染与防腐剂使用情况关系的探讨

为了解涂料的微生物污染与防腐剂使用情况之间的关系,按照ISO 9252-1989(E)检测207件市售涂料微生物指标,利用高效液相色谱检测有微生物检出涂料和40件无微生物检出涂料的防腐剂使用情况。结果发现有12件涂料微生物超标;异噻唑啉酮类防腐剂是本实验检出使用最多的防腐剂;微生物超标涂料防腐剂含量比正常低或者未检测到,种类单一。涂料的防腐剂使用情况与微生物污染程度有着密切的联系,建议建立和完善涂料限用防腐剂标准,指导涂料企业安全生产和质量监督。     

Short-term effect of silicone gel on peripheral nerves: a histologic study.

The effect of silicone gel on the peripheral nerve was studied in Sprague-Dawley rats. Silicone gel was placed either extraneurally (N = 36) adjacent to or injected directly in the sciatic nerve (N = 20). Nerve histology was studied every 2 weeks over a 20-week period. Extraneural silicone gel elicited an intense inflammatory response characterized initially by predominantly histiocytes with a few eosinophils, lymphocytes, and foreign-body giant cells. The cellular response peaked at 4 weeks, after which time collagen deposition increased and the thickness of the cellular infiltrate surrounding the gel decreased. The gel was temporarily contained by the inflammatory response, but throughout the time course of the study, gel migration and breakup into smaller droplets occurred. Each droplet appeared to initiate the inflammation-fibrosis cycle anew. Perineural fibrosis was marked by 20 weeks, but there was no penetration of the epineurium by the gel. Intraneurally injected silicone gel also caused a delayed, but similar inflammatory response, eventually followed by fibrosis surrounding the gel. Intraneural gel tended to remain in larger droplets and did not migrate over the duration of this study. No direct evidence of gel toxicity to peripheral nerves was observed in either the extraneural or intraneural gel groups despite the initial intense inflammatory response and subsequent fibrosis.     

The functional consequences of mutualistic network architecture

The architecture and properties of many complex networks play a significant role in the functioning of the systems they describe. Recently, complex network theory has been applied to ecological entities, like food webs or mutualistic plant-animal interactions. Unfortunately, we still lack an accurate view of the relationship between the architecture and functioning of ecological networks. In this study we explore this link by building individual-based pollination networks from eight Erysimum mediohispanicum (Brassicaceae) populations. In these individual-based networks, each individual plant in a population was considered a node, and was connected by means of undirected links to conspecifics sharing pollinators. The architecture of these unipartite networks was described by means of nestedness, connectivity and transitivity. Network functioning was estimated by quantifying the performance of the population described by each network as the number of per-capita juvenile plants produced per population. We found a consistent relationship between the topology of the networks and their functioning, since variation across populations in the average per-capita production of juvenile plants was positively and significantly related with network nestedness, connectivity and clustering. Subtle changes in the composition of diverse pollinator assemblages can drive major consequences for plant population performance and local persistence through modifications in the structure of the inter-plant pollination networks.     

Structure-property relationships for three indoline dyes used in dye-sensitized solar cells: TDDFT study of visible absorption and photoinduced charge-transfer processes

The electronic structures of three D-A-π-A indoline dyes (WS-2, WS-6, and WS-11) used in dye-sensitized solar cells (DSSCs) were studied by performing quantum chemistry calculations. The coplanarity of the A-π-A segment and distinct noncoplanarity of the indoline donor part of each dye were confirmed by checking the calculated geometric parameters. The relationships between molecular modifications and the optical properties of the dyes were derived in terms of the partial density of states, absorption spectrum, frontier molecular orbital, and excited-state charge transfer. 3D real-space analysis of the transition density (TD) and charge difference density (CDD) was also performed to further investigate the excited-state features of the molecular systems, as they provide visualized physical pictures of the charge separation and transfer. It was found that modifying the alkyl chain of the bridge unit near the acceptor unit is an efficient way to decrease dye aggregation and improve DSSC efficiency. Inserting a hexylthiophene group next to the donor unit leads to a complicated molecular structure and a decrease in the charge-transfer ability of the system, which has an unfavorable impact on DSSC performance.     

The rate of attachment of amoebae to the substratum: a study of nuclear-cytoplasmic relationships

The rate of attachment to the substratum was found to be a strain specific character of certain large free-living amoebae. Two strains, which differed significantly in this respect, were compared with regard to the rate of attachment of enucleated cytoplasm, nuclear-cytoplasmic hybrids and amoebae injected with cytoplasm from another strain. It was found that both the nucleus and the cytoplasm of the more rapidly attaching strain were able to transmit this character to amoebae of the more slowly attaching strain. The possible mechanisms underlying attachment and transmission of the rate of attachment are discussed.