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Nonionic surfactants used in agri-spraying processes may cause varying degrees of corneal irritation when they come in direct contact with farmers' eyes, and the exact irritations are thought to be determined by how surfactants interact with corneal cell membranes. However, how nonionic surfactants interact with cell membranes at the molecular and nano levels remains largely unexplored. In this study, the interactions between nonionic surfactants (alkyl ethoxylate, C12Em) and lipid membranes were examined by membrane permeability measurement, quartz crystal microbalance with dissipation, dual polarization interferometry, confocal laser scanning microscopy, and neutron reflection, aiming to reveal complementary structural features at the molecular and nano levels. Apart from the extremely hydrophobic surfactant C12E2, all nonionic surfactants studied could penetrate the model cell membrane composed of a phosphocholine lipid bilayer. Nonionic surfactants with intermediate amphiphilicity (C12E6) rapidly fused into the lipid membrane and stimulated the formation of pores across the lipid bilayer, consistent with the cytoplasm leakage and fast cell necrosis observed from the cytotoxicity study of corneal cells. In comparison, while hydrophobic and hydrophilic surfactants [those with long and short ethoxylates (C12E4,12,23)] could cause mild structural alteration to the outer lipid layer of the membrane, these structural changes were insufficient to elicit large cytoplasmic leakage rapidly and instead cell death occurred over longer periods of time due to changes in the membrane permeability. These results reveal the strong link of surfactant-lipid membrane interactions to surfactant cytotoxicity and the association with amphiphilicity of nonionic surfactants.

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HYPOTHESIS: Nonionic surfactants are widely used as co-formulants in agrochemical sprays. During spraying, they may come into direct contact with humans and animals, causing irritation in different tissues. However, how the molecular structures of these surfactants affect their toxicity towards human eye and skin at the cellular level has not been well characterised. EXPERIMENT: In this study, the cytotoxicities of two sets of nonionic surfactants (alkyl ethoxylate, CnEm) against human corneal and skin cell lines were examined, with one set composed of varied surfactant head length but fixed tail length (C12E4-23) and the other set oppositely composed (C10-16E6). The cell viability and morphology against different nonionic surfactants for varied exposure times were studied, followed by characterisation of their membrane-lytic ability. FINDING: Nonionic surfactants with intermediate amphiphilicity killed cells rapidly due to their strong membrane-lytic power. Those with weak or strong hydrophobicity exhibited low cytotoxicity but had different modes of action depending on their hydrophobicity. Hydrophobic surfactants were found to adsorb on to cell membranes with no observed structural damage for 2 hr. Hydrophilic surfactants were also found to adsorb on to cell membranes but did cause mild structural changes. While the changes were not sufficient to elicit large cytoplasmic leakage over short periods of time, membrane associations did cause cell shrinkage which eventually resulted in cell death over longer exposure periods. These results revealed that the specific amphiphilic nature of nonionic surfactants played a crucial role in determining their cytotoxicity. This work provided a useful basis for the assessment of amphiphilicity of the nonionic surfactants used in agrochemical sprays by balancing their efficiency, toxicity and environmental impact.

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HYPOTHESIS: Nonionic alkyl ethoxylate surfactants are widely used in agrochemicals to facilitate the permeation of systemic herbicides and fungicides across the plant waxy film. Industrial grade surfactants are often highly mixed and how the mixing affects their interactions with pesticides and wax films remains largely unexplored. A better understanding could enable design of mixed nonionic surfactants for herbicides and fungicides to maximize their efficiency and reduce wastage whilst controlling their impact on plant wax films. EXPERIMENT: In this study, nonionic surfactants with general structure n-oxyethylene glycol monododecyl ether (C12En) were used to form surfactant mixtures with the same average ethoxylate numbers but different hydrophilic-lipophilic balance (HLB) values. Their mixed micellar systems were then used to solubilize a herbicide diuron (DN) and a fungicide cyprodinil (CP), followed by plant wax solubilization upon contact with wax films. These processes were monitored by 1H NMR and SANS. FINDING: Pesticide solubilization made surfactant micelles effectively more hydrophobic but subsequent wax dissolution caused pesticide release and the restoration of the micellar amphiphilicity. Nonionic surfactants with lower HLBs form larger nanoaggregates, show enhanced wettability, and have better ability to solubilize and permeate pesticides across the wax film, but may cause significant damage to plant growth. These observations help explain why herbicides applied on weeds would benefit from surfactants with lower HLB values while fungicides require surfactants with HLBs to balance between delivery efficiency and potential phytotoxicity risks.

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HYPOTHESIS: Surfactants have been widely used as adjuvants in agri-sprays to enhance the solubility of pesticides in foliar spray deposits and their mobility through leaf cuticles. Previously, we have characterised pesticide solubilisation in nonionic surfactant micelles, but what happens when pesticides become solubilised in anionic, cationic and zwitterionic and their mixtures with nonionic surfactants remain poorly characterised. EXPERIMENTS: To facilitate characterisations by SANS and NMR, we used nonionic surfactant hexaethylene glycol monododecyl ether (C12E6), anionic sodium dodecylsulphate (SDS), cationic dodecyltrimethylammonium bromide (DTAB) and zwitterionic dodecylphosphocholine (C12PC) as model adjuvant systems to solubilise 3 pesticides, Cyprodinil (CP), Azoxystrobin (AZ) and Difenoconazole (DF), representing different structural features. The investigation focused on the influence of solubilisates in driving changes to the micellar nanostructures in the absence or presence of electrolytes. NMR and NOESY were applied to investigate the solubility and location of each pesticide in the micelles. SANS was used to reveal subtle changes to the micellar structures due to pesticide solubilisation with and without electrolytes. FINDINGS: Unlike nonionic surfactants, the ionic and zwitterionic surfactant micellar structures remain unchanged upon pesticide solubilisation. Electrolytes slightly elongate the ionic surfactant micelles but have no effect on nonionic and zwitterionic surfactants. Pesticide solubilisation could alter the structures of the binary mixtures of ionic/zwitterionic and ionic/nonionic micelles by causing elongation, shell shrinkage and dehydration, with the exact alteration being determined by the molar ratio in the mixture.

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HYPOTHESIS: Surfactants are widely used in agri-sprays to improve pesticide efficiency, but the mechanism underlying their interactions with the surface wax film on plants remains poorly understood. To facilitate physical characterisations, we have reconstituted wheat cuticular wax films onto an optically flat silicon substrate with and without octadecyltrimethoxysilane modification to control surface hydrophobicity. EXPERIMENTS: Imaging techniques including scanning electron microscopy (SEM) unravelled morphological features of the reconstituted wax films similar to those on leaves, showing little impact from the different substrates used. Neutron reflection (NR) established that reconstituted wax films were comprised of an underlying wax film decorated with top surface wax protrusions, a common feature irrespective of substrate hydrophobicity and highly consistent with what was observed from natural wax films. NR measurements, with the help of isotopic H/D substitutions to modify the scattering contributions of the wax and solvent, revealed different wax regimes within the wax films, illustrating the impact of surface hydrophilicity on the nanostructures within the wax films. FINDINGS: It was observed from both spectroscopic ellipsometry and NR measurements that wax films formed on the hydrophobic substrate were more robust and durable against attack by nonionic surfactant C12E6 solubilised with pesticide Cyprodinil (CP) than films coated on the bare hydrophilic silica. Thus, the former could be a more feasible model for studying the wax-surfactant-pesticide interactions.

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HYPOTHESIS: Nonionic surfactants are used as adjuvants in agri-sprays to stabilise pesticides, but what happens when pesticide-loaded micelles are brought into direct contact with plant leaves? As pesticide solubilisation dehydrates the micellar shell and increases the effective hydrophobicity of the surfactant, we hypothesise that these micelles would uptake plant waxes and alter the amount of pesticide solubilized as a result of the re-equilibrating process. EXPERIMENTS: The solubility of the pesticide cyprodinil (CP) and its effect on the shape of hexaethylene glycol monododecyl ether (C12E6) micelles were studied using changes in cloud point, nuclear magnetic resonance (NMR), cryogenic transmission electron microscopy (Cryo-TEM) and small-angle neutron scattering (SANS). Similarly, the solubility of wheat leaf waxes was examined, as was the effect of adding leaf waxes to pre-dissolved cyprodinil in micellar C12E6. FINDINGS: Wax solubilisation caused pesticide release and shell hydration, and shortened the length of the cylindrical micelles of the CP loaded C12E6. Temperature increase led to a significant rise in the amount of the dissolved waxes, increased pesticide release, increased micellar length, and caused shrinkage and dehydration of the shell. This study indicates that agrochemical sprays are capable of dissolving leaf waxes, and may trigger pesticide release from surfactant micelles upon contact with plant surfaces.

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Nonionic surfactants have been widely used in agri-sprays to enhance the solubility and mobility of pesticides, but what happens when pesticides become solubilized into surfactant micelles remains poorly characterized. To facilitate physical characterisations, we used the nonionic surfactant hexaethylene glycol monododecyl ether (C12E6) as a model system to solubilize 4 pesticides including Cyprodinil (CP), Diuron (DN), Azoxystrobin (AZ) and Difenoconazole (DF). The investigation focused on the influence of solubilizate and temperature in driving changes to the micellar nanostructures. Dynamic light scattering (DLS), cryogenic transmission electron microscopy (Cryo-TEM) and small-angle neutron scattering (SANS) measurements were used to reveal changes to the micellar structure before and after pesticide solubilisation. Nuclear magnetic resonance (NMR) was also applied to investigate the solubility and location of each pesticide in the micelles. Pesticides clearly altered the micellar structure, by increasing the aggregation number and micellar lengths, whilst shrinking and dehydrating the shells, leading to a consequent decrease in the dispersion cloud points. Increases in temperature affected micellar structures in a similar way. Thus, temperature increases and the solubilisation of pesticides can both make the surfactant effectively more hydrophobic, altering the micellar nanostructures and shifting the pesticide location within the micelles. These changes subsequently implicate how pesticides are delivered into plants through the natural wax films.

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Small-angle neutron scattering (SANS) was used to investigate the size and shape of zwitterionic dodecyl phosphocholine (C12PC) micelles formed at various concentrations above its critical micelle concentration (CMC = 0.91 mM). The predominant spherical shape of micelles is revealed by SANS while the average micellar size was found to be broadly consistent with the hydrodynamic diameters determined by dynamic light scattering (DLS). Cryogenic tunneling electron microscopy (cryo-TEM) shows a uniform distribution of structures, proposing micelle monodispersity ( Supporting Information ). H/D substitution was utilized to selectively label the chain, head, or entire surfactant so that structural distributions within the micellar assembly could be investigated using fully protonated, head-deuterated, and tail-deuterated PC surfactants in D2O and fully deuterated surfactants in H2O. Using the analysis software we have developed, the four C12PC contrasts at a given concentration were simultaneously analyzed using various core-shell models consisting of a hydrophobic core and a shell representing hydrated polar headgroups. Results show that at 10 mM, C12PC micelles can be well represented by a spherical core-shell model with a core radius and shell thicknesses of 16.9 ± 0.5 and 10.2 ± 2.0 Å (total radius 27.1 ± 2.0 Å), respectively, with a surfactant aggregation number of 57 ± 5. As the concentration was increased, the SANS data revealed an increase in core-shell mixing, characterized by the emergence of an intermediate mixing region at the spherical core-shell interface. C12PC micelles at 100 mM were found to have a core radius and shell thicknesses of 19.6 ± 0.5 and 7.8 ± 2.0 Å, with an intermediate mixing region of 3.0 ± 0.5 Å. Further reduction in the shell thickness with concentration was also observed, coupled with an increased mixing of the core and shell regions and a reduction in miceller hydration, suggesting that concentration has a significant influence on surfactant packing and aggregation within micelles.

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Nonionic alkyl ethoxylates (C(n)E(m)) have been extensively studied for their adsorption, aggregation, and solubilization individually and in small groups. In this work, we report a more systematic study of the effects of alkyl chain (tail) and ethoxylate (head) length on the size, shape, and extent of intermixing within the C(n)E(m) micelles in aqueous solution. Data from small angle neutron scattering (SANS) and nuclear magnetic resonance (NMR) were combined to undertake the structural characterization of micelles formed from the two separate series of surfactants C(n)E6 (n = 10, 12, 14) and C12E(m) (m = 5, 6, 8, 10, 12). The micellar core volume (V(core)) could be well determined with reasonable accuracy and linked to the hydrophilic-lipophilic balance (HLB) of the surfactant, with a sharp size and shape transition occurring around HLB = 12.5. NOESY NMR results revealed protrusions of the terminal methylene groups into the ethoxylate shell, thus providing direct experimental evidence for the phenomenon of "roughness" or intermixing of the core-shell interface. These detailed studies are compared with previous investigations on this model surfactant system.

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This study reports the development and use of a novel thermoresponsive polymeric nanofilm for controlling cell adhesion and growth at 37 °C, and then cell detachment for cell recovery by subsequent temperature drop to the ambient temperature, without enzymatic cleavage or mechanical scraping. A copolymer, poly(N-isopropylacrylamide-co-hydroxypropyl methacrylate-co-3-(trimethoxysilyl)propyl methacrylate) (abbreviated PNIPAAm copolymer), was synthesized by free radical polymerization. The thermoresponses of the copolymer in aqueous solution were demonstrated by dynamic light scattering (DLS) through detecting the sensitive changes of copolymer aggregation against temperature. The DLS measurements revealed the lower critical solution temperature (LCST) at approximately 30 °C. The PNIPAAm film stability and robustness was provided through silyl cross-linking within the film and with the hydroxyl groups on the substrate surface. Film thickness, stability, and reversibility with respect to temperature switches were examined by spectroscopic ellipsometry (SE), atomic force microscopy (AFM), and contact angle measurements. The results confirmed the high extent of thermosensitivity and structural restoration based on the alterations of film thickness and surface wettability. The effective control of adhesion, growth, and detachment of HeLa and HEK293 cells demonstrated the physical controllability and cellular compatibility of the copolymer nanofilms. These PNIPAAm copolymer nanofilms could open up a convenient interfacial mediation for cell film production and cell expansion by nonenzymatic and nonmechanical cell recovery.

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