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Aggregation and Rheological Behavior of the Lavender oilPluronic P123 microemulsions in water-ethanol mixed solvents Oyais Ahmad Chat, Nighat Nazir, Parvaiz Ahmad Bhat, Puthusserickal Abdulrahiman Hassan, Vinod Kumar Aswal, and Aijaz Ahmad Dar Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.7b02845 • Publication Date (Web): 20 Nov 2017 Downloaded from http://pubs.acs.org on November 22, 2017

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Aggregation and Rheological Behavior of the Lavender oil-Pluronic P123 microemulsions in water-ethanol mixed solvents Oyais Ahmad Chat,a,b Nighat Nazirc, Parvaiz Ahmad Bhat, a,b P.A. Hassan,d V.K. Aswal,e Aijaz Ahmad Dara,* a

Physical Chemistry Division. Department of Chemistry, University of Kashmir, Srinagar-190006, J&K, India.

b

Department of Chemistry, Government Degree College Pulwama-192301, J & K, India

c

Department of Chemistry, Islamia College of Science and Commerce, Hawal, Srinagar-190002, India

d

Chemistry Division, Bhabha Atomic Research Centre, Mumbai – 400 085, India

e

Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai – 400 085, India

Corresponding Author A.A. Dar, Fax: + 91- 1942414049; Tel: + 91- 9906417902. Email:[email protected], [email protected]

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ABSTRACT The effect of lavender oil on aggregation characteristics of P123 in aqueous-ethanolic solutions is investigated systematically by DLS, SANS and Rheology. The solubilization capacity of the formulation increased by increasing P123 concentration. The study unveiled the importance of the short chain alcohol-ethanol, as solubilization enhancer. The apparent hydrodynamic radius (Rh) increased significantly with increase in lavender oil concentration up to maximum oil solubilization capacity of the copolymer at a particular ethanol concentration. DLS measurements on 5, 10 and 15 wt% P123 in the presence of 25 % ethanol revealed the presence of large sized micellar clusters in addition to the oil swollen micelles. The core size (RC), radius of hard sphere (RHS) and aggregation number (N) obtained from SANS profiles showed considerable enhancement with the addition of lavender oil confirming penetration of oil inside the copolymer. Rheological studies showed that viscosity also increased significantly with the addition of Lavender oil near maximum loading limit of the copolymer. Quite interestingly, the sol-gel transition temperature displayed strong dependence on both P123 as well as oil concentration and decreased almost linearly by increasing oil concentration. This study demonstrates the use of biocompatible and temperature sensitive self-assembled system for Lavender oil solubilization that are beneficial in cosmetic industry wherein controlled release, of fragrances etc. is demanded. Keywords: Lavender Oil, Pluronic, Solubilization; SANS, Rheology


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1. Introduction

Lavender oil (Lavandula angustifolia) is a versatile and extensively used essential oil containing hundreds of components,1 having predominance of linalool, linalyl acetate, lavandulyl acetate, camphor and 1,8-cineole.2 The fragrant oil extracted from lavender is commercially relevant for its therapeutic properties, like anti-inflammatory, antiseptic, antiviral, anticonvulsive, antibacterial, antidepressant, and antioxidant.3,

4, 5, 6

The unique chemical composition and

delightful aroma makes it suitable for use in wide range of food products7, aromatherapy8,3 and cosmetics.9 The stability and long-lasting perception of the fragrant molecules are crucial for their acceptance in food and perfumery industries.10, 11,12 The constituents of such oils are known to be hydrophobic, highly volatile, chemically unstable and prone to oxidative degradation.10 A loss of volatile compounds, declines their commercial value.12 Therefore, special aqueous based solubilization and delivery systems13, 14, 15, 16, 17 18, 19 have been proposed for fragrant molecules to thwart their chemical instability, enhance their water solubility and decrease their volatility for persistent fragrance over longer times. Surfactant aided microencapsulation is becoming increasingly important owing to its capability for solubilization, stabilization and controlled transport of volatile fragrant molecules. 20, 21, 22, 23 24, 25, 26, 27, 28 Recently neutron reflectivity was utilized by Bradbury et al.29, 30 and Penfold et al.

31, 32

to explore the co-adsorption at the air-

solution interface of some perfume molecules for optimizing their performance in different formulations. Amphiphilic association structures reduce rate of evaporation of volatile molecules by reducing the vapor pressure, prolong longevity of fragrance perception and favor their persistence.33, 34, 35, 36, 37, 38 Amphiphilic block copolymers based physical delivery systems have also been used to stabilize sensitive fragrant compounds in water.39 40, 41 Block copolymer micelles have been found to be superior to the micelles of conventional surfactants due to their better solubilization capability, having significant stability at low concentrations and possessing long dissociation time (hours/ days) because of their significant thermodynamic and kinetic stabilities. 42, 43, 44

Although, Pluronic copolymer micelles have been used in aqueous solutions to encapsulate

model fragrant molecules like benzyl formate,45 limonene46 and linalool,33 detailed microstructural investigations have been scarcely done. The phase behaviour of ethanolic solution of Pluronics has been subject of several studies 47, 48, 49 but very rare reports are available in the literature where such systems have been employed for solubilization studies and effect of solubilizate on the 3 ACS Paragon Plus Environment

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aggregation behaviour of Pluronics in ethanolic solvents. Berthier et al.39 have studied the impact of block copolymers on the volatility of fragrant molecules in ethanolic solution where a positive interaction between such molecules and polymers is essential for controlled release of perfume solutes. Also, pluronic-oil systems have been studied in aqueous solution to investigate the effect of oils like m-xylene, octane, toluene, benzene, hexane, cyclohexane on the aggregation behaviour of Pluronics. It has been shown that oils are significant in altering the physico-chemical characteristics of copolymer solutions.50 However, to the best of our knowledge no report was found in the literature about solubilization of essential oils like lavender oil (Kashmir) in aqueousethanolic P123 vis-a-vis solubilizate induced microstructural evolution of surfactant solutions and hence their associated phase behavior. The aim of the current work was to characterize P123 based bio-compatible solubilization medium for solubilization of lavender oil. The aggregation features of P123 in the presence of oil and ethanol were investigated using DLS, SANS and Rheology. The results show that such nanocarriers can prove potential candidates in the controlled perfume release applications.

2.Materials and methods 2.1. Materials Triblock Copolymer Pluronic P123 (EO20PO70EO20) was procured from Sigma Aldrich. Lavender oil was obtained from Indian Institute of Integrative Medicine (IIIM), Srinagar, J&K, India. High Linalool (25.27%) and Linalyl acetate (44.98%) of Lavender cultivated in Jammu and Kashmir, India is indicative of its international quality.51 Ethanol was a Merck product. The deionized water ( 18 MΩ cm) was employed to prepare samples for DLS and Rheological investigations while as D2O (99.4 atom % D purity) was used to prepare samples for SANS measurements.The stock solution of P123 20 % (w/w) was kept in refrigerator for one week for equilibration. Various samples were prepared by appropriate mixing of P123, ethanol and oil. After adding oil, samples were heated to ensure complete solubilization of oil. 2.2. Methods 2.2.1. Dynamic Light Scattering Malvern 4800 Autosizer (7132 digital correlator) was used for DLS measurements . with He-Ne laser as the light source worked at 632.8 nm . For unimodal distribution of relaxation time52 the modified cumulant method53 was employed to analyze the electric field autocorrelation function, 4 ACS Paragon Plus Environment

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g1() vs. time data for evaluation of the average decay rate while as CONTIN,54 was employed in all other cases The data was recorded at 130o ∝

𝑔1 (𝜏) = ∫−∝ 𝐴()𝑒

−𝑡⁄ 

𝑑(𝑙𝑛)

(1)

The diffusion coefficient values (D) were evaluated by fitting the autocorrelation to . g1().Stokes - Einstein equation. was then used to determine Rh of the micelles 𝑘 𝑇

𝐷 = 6𝐵𝑅

ℎ

(2)

All the measurements were performed at scattering angle of 130o and at constant temperature (30± 0.1 oC). 2.2.2. Small Angle Neutron Scattering SANS measurements were performed using SANS diffractometer at Dhruva reactor, Bhabha Atomic Research Centre, Trombay, India. The idea about the structure and nature of the interaction between pluronic micelles in the presence of Lavender oil and ethanol was obtained from SANS data done for the systems 5% P123+15 Ethanol, 5% P123+25% Ethanol and 15% P123+25% Ethanol at 30 and 50 oC in D2O. The details of SANS analysis are given in Supporting Information (SI). 2.2.3. Steady State Fluorescence The fluorescence measurements in P123 were done employing RF-5301-PC Flourimeter ( Shimadzu) at 30 oC. Pyrene was used as probe to ascertain formation of copolymers/surfactant micelles.55 Pyrene (2.5 µM.) was excited at 332 nm with slit width of 3 nm..

2.2.4. Rheology Rheological measurements were done employing Rheometer from Anton Paar (MCR-102 )using CP-50, measuring system. The flow behavior of P123 in presence and absence of Lavender oil was obtained using steady shear tests at 30 oC. The temperature responsiveness of the ternary (P123, ethanol and Lavender oil) was determined using dynamic temperature measurements with incremental heating rate (1 °C/min). The temperature sweep tests were done in LVR regime at shear stress of 1 Pa and oscillation frequency of 1 Hz. All experiments repeated twice with good reproducibility. 3.Results and discussion 3.1. Microstructure by DLS and SANS 5 ACS Paragon Plus Environment

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An increase in micellar core size and aggregation number on account of dehydration and consequent restructuring in aqueous P123 ensues sphere to rod transition/growth, near clod point.56 To gain an insight into the lavender oil induced micellar reorganization and growth processes in the presence of ethanol, we studied solubilization of lavender oil in various P123 concentrations at different ethanol percentages by DLS. The addition of ethanol was necessary to impart solubilization of lavender oil, as it was observed that pure aqueous P123 was unable to dissolve the oil in sufficient amounts. 3.1.1. Effect of Ethanol Concentration The changes in microstructure of the P123 micelles due to solubilization of lavender oil at various copolymer and ethanol compositions was screened using DLS. Fig. 1 depicts evolution of correlation function (Fig. 1a) and corresponding size distribution plots (Fig. 1b) of 5 wt% P123 (5P) with the addition of lavender oil at 15% v/v (15E) ethanol. It is clearly evident (Fig. 1a) that the relaxation of the correlation function shifts towards long time with increase in lavender oil concentration suggesting enhancement in apparent P123 micellar size with increase in Lavender oil concentration. The size distribution plots presented in Fig. 1b clearly indicate increase in average apparent hydrodynamic diameter (2Rh) of P123 from 23.4 nm to 144 nm with increase in oil from 0 to 1.32 % (v/v). With further addition of the oil, the average hydrodynamic diameter remains nearly constant followed by phase separation of excess oil. This concentration of oil has been taken as the maximal solubility of the oil in the P123-ethanol systems. The increase in micellar size can be related to swelling of micellar core and corona due to solubilization of oil within P123 micelles. The variation in DLS data support the view point that aggregation characteristics of P123 change significantly in the presence of the oil, leading to an increase in micellar size with the addition of lavender oil. In order to understand the influence of ethanol concentration on P123 mediated solubilization of lavender oil, DLS studies were carried out with constant P123 of 5 wt% (5P) but at varying ethanol compositions, 20% v/v (20E) and 25% v/v (25E). Perusal of intensity correlation function reveals that the size distribution for 5P+20E system show similar dependence on lavender oil (% v/v) as observed for 5P+15E system i.e., the correlation function shifts to longer time scale (figure not shown) with concomitant increase in apparent hydrodynamic diameter (2Rh) from 24 nm to 234 nm with increase in lavender oil from 0 to 1.32% v/v. A further increase in oil percentage results in clouding (phase separation) and hence DLS experiments could not be performed beyond this oil content. 6 ACS Paragon Plus Environment

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Solubilization at higher ethanol percentage (25% v/v) but at same percentage of P123 (5% wt), 5P+25E system, showed that the relaxation of correlation function for 5P+25E shifts to longer time scale with the addition of oil, as observed in case of 5P+15E and 5P+20E systems but with a difference that the polydispersity in size distribution is much higher. Analysis of the correlation function using CONTIN algorithm suggests bimodal distribution with the addition of lavender oil to 5P+25E system and therefore indicate the presence of two types of aggregates in this system. This could arise from the presence of micelles as well as clusters of micelles from attractive interaction of the micelles. The apparent diameter (2Rh) of the micelles increased from 27.4 nm to 84.9 nm at 0 and 1.32 % oil (v/v) respectively. It is important to note here that increase in ethanol concentration at constant P123 concentration did not improve solubilization efficiency of the system but affected the structure quite significantly (Fig. 1S). The variation in the average hydrodynamic diameter with oil concentration for 5P + 15E, 5P+20E and 5P+25E systems are presented in Fig. 2. The apparent hydrodynamic radius (Rh) in the presence of ethanol are larger compared to that in pure aqueous system due to possible stretching of corona and core.47 Lavender oil molecules get entrapped in the micellar pseudo-phase, the micellar core swells significantly and results in the observed growth of the micelle. It is pertinent to mention that Kashmir based lavender oil is composed of as many as 53 components of varying percentage with Linalool (25.27%) and Linalyl acetate (44.98%) constituting 70% of the total composition.51 It appears that the oil components are solubilized mainly in micellar core and some small fraction in corona region depending on the polarity of the constituent molecules. The consequences of the addition of lavender oil on the micellization of P123 in ethanol water mixture, we evaluated CMC using pyrene as a probe (Fig. 2S). The sensitivity of pyrene intensity ratio I1/I3 to hydrophobicity of the surrounding environment was used to ascertain presence of micelles. Our results (Fig. 2S) suggest that CMC decreases with the addition of lavender oil at constant P123: Ethanol (1:3) ratio. Therefore, it is presumed that the addition of oil dehydrates the PEO/PPO chains making the system hydrophobic and increases its entropy due to release of structured solvent. As a result of higher hydrophobicity, the oil laden P123 micellizes early and shows lower CMT (allowing micellization at low temperatures).50 The dehydration of the micelle corona facilitate attractive interactions among micelles leading to the formation of clusters, as revealed by the secondary structures in 5P+25E system. The above observations are further substantiated by SANS. If we consider the SANS plots in Fig. 3 in absence of oil, the absence of intermicellar interactions (i.e., S(Q) = 1) is validated by the 7 ACS Paragon Plus Environment

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absence of any correlation peak. From the analysis, employing a monodisperse spherical core, we observed core radius of 5.4 nm and 4.8 nm respectively for 5P+15E and 5P+25E in the absence of oil. It is pertinent to mention that the shell contribution was neglected owing to very low contrast with the solvent. SANS data for 5 % copolymer at varying ethanol concentrations, Fig. 3, were evaluated in terms of spherical form factors of the hydrophobic micellar core owing to absence of interparticle interactions at such copolymer concentration,57 the corresponding results is given in Table 1. A steady decrease in the micellar core radius (Rc), aggregation number (N) and hard sphere radius (RHS) (Table 1) is observed with increase in ethanol concentration. Unlike water , ethanol, is considered good solvent for both PO and EO blocks and consequences in an increase in CMC, CMT, CP and decrease in aggregation number57, 58, 59 If we compare SANS spectra of 5P at 15E (Fig. 3a) and 25E (Fig. 3b) in absence of oil, the reduction in scattering intensity at low Q values with ethanol addition confirms diminution micellar size. 3.1.2. Effect of P123 Concentration The solubilization capability of a given P123 solution toward the lavender oil was not enhanced much by increasing amount of ethanol as discussed in previous section (Fig. 1S). To investigate the impact of increasing P123 concentration on solubilization of lavender oil and the corresponding microstructural changes in P123 aggregates, we performed the experiments with 10 and 15 wt% P123 at constant ethanol concentration (25% v/v) referred hereafter as 10P+25E and 15P+25E respectively. The DLS results for 10P+25E and 15P+25E are presented in Fig. 3S. With an increase in P123 content, the solubilization capability of the micelles increased significantly (Fig. 3S). It is interesting to note that the correlation function (Fig. 4S), like for other cases, shifts to longer time scale but nature of the correlogram changes significantly, with prominent slow mode of relaxation. The system being multicomponent, it is difficult to assign such behavior to a particular phenomenon. The CONTIN analysis of the data revealed the existence of twofold aggregates with widely different relaxation times, the fast (small Rh) and slow (large Rh) relaxation assigned respectively to the micelles and clusters as observed in some other cases at higher concentration of Pluronics. The apparent 2RH corresponding to the fast mode increased from 25 nm to 72 nm with increase in concentration of lavender oil from 0to 2.6 % v/v without appearance of clouding at the experimental temperature of 30 oC. From solubilization point of view (Fig. 3S), higher solubilization efficiency was observed for 10P+25E system compared to 5P+25E system about 2.6% (v/v) oil could be loaded in former compared to maximum of 1.64% (v/v) in the latter. 8 ACS Paragon Plus Environment

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An increase in P123 concentration to 15 wt % in the presence of 25% v/v ethanol i.e., 15P+25E, improved the solubilization efficiency further. Among all systems screened, 15P+25E displayed highest solubilization of about 3.85% (v/v) of oil without being phase separated. As observed from the figure Fig. 3Sc, the apparent 2Rh increases from 23 nm to 48 nm only with increase in oil from 0 to 3.85% (v/v) for 15P+25E system. The incorporation of oil molecules and the consequent growth of P123 micelles can been correlated mainly to the dehydration of PPO chains. The dehydrated micelles are more hydrophobic and therefore favour micellization. The important outcome of DLS results is that lavender oil gets entrapped into P123 micelles and affects the aggregation behavior of the P123 micelles significantly. In addition, the oil solubilization was found to be dependent on P123 concentration at a given ethanol composition. Similar results were obtained from SANS experiments. The correlation peak (Q) in the SANS profile of 15P+25E (Fig. 4) is observed, in contrast to 5P system (Fig 3). This is a manifestation of reduced intermicellar distance (d) on account of enhanced number density of micelles.57 The analysis of SANS spectra of 15% (w/w) copolymer solution using hard sphere potential was done assuming Q and d related as d  2/Qmax,. Micellar core described by intraparticle form factor (P(Q)), total overall micellar dimensions and volume fraction taken care by the interparticle interaction (S(Q)). The volume and Rc of PO units (95.4 Å3) were employed to obtain the micellar aggregation number assuming micellar core to consist of PO blocks only. The overall hard sphere micellar radius (from SANS) were observed to be smaller than hydrodynamic radius (from DLS). This may be a manifestation of movement of the micelles along with solvent sheath.57 Also, the lower agreement of apparent hydrodynamic radius of polydisperse micelles to the sum of average core and shell thickness is primarily because of the large scattering contributions (sixth power of radius) from big particles in DLS. Since SANS analysis is performed using a limited Q range (lowest Q being 0.018 Å-1), any contributions from scattering objects larger than 2*/Qmin will make negligible contributions to the model fitting. However, this is not the case for DLS due to long wavelength of light and it relies on time dependence of scattered intensity. Therefore, it is likely that the reported increase in the apparent hydrodynamic radius arises from the large polydispersity in size and consequent bias towards larger sizes. In addition, a linearity in the low Q data on the log-log scale confirms the micellar clusters as it is signature for existence of such clusters.56, 60


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The influence of lavender oil on SANS pattern (Fig. 4) is significant, scattering intensity increases significantly with an increase in oil concentration for all the three systems 5P+15E, 5P+25E, and 15P+25E. The scrutiny of the data (Table 1) reveals that with increase in concentration of lavender oil, a progressive increase in the RC, RHS and N is observed. Because the oil molecules are mainly solubilized in the micellar core, additional oil molecules are encapsulated in the micelles with the increase in oil concentration resulting in significant distension of the micellar core. On the contrary, the micellar mole fraction (and number density of micelles (n) decrease progressively with the addition of lavender oil in all systems. The reduced number density of micelles due to growth of micelles by the solubilized oil leads to decrease in average hydration of micelles and as a result the micellar mole fraction is decreased. For 15P+25E system, the enhancement in scattering intensity with the addition of oil is accompanied by correlation peak (Qmax) shift to low Q values. This indicates that intermicellar distance increases upon the addition of oil due to decrease in the number density and/or increase in aggregation number or swelling of P123 micelles. The solubilization of lavender oil and the resultant swelling of the P123 micelles is schematically presented in Scheme 1. 3.1.3. Effect of temperature To know the consequence of temperature on micelle structure, SANS experiments were performed on selected formulations at different temperatures. A comparison of SANS patterns of the three systems (5P+15E, 5P+25E, and 15P+25E) at two different temperatures (30 oC and 50 oC) in the presence and absence of oil is presented in Fig. 5. The patterns reveal a significant upsurge in scattering intensity and a shift in Qmax to lower Q with increase in temperature, was also observed for 15P+25E system. This indicates a temperature induced growth of P123 micelles, which correlate well with the similar reports in literature that occurs due to the transition of micelles to prolate ellispsoids.57 The effect of temperature on the obtained micellar parameters are provided in Table 2. The aggregation of P123 micelles is improved both in the presence of oil and with increase in temperature from 30 oC to 50 oC as depicted by increase in RC, RHS, and N, while as and n decrease with the increase in temperature. The increase in temperature causes PPO chains to stretch, as a result of which the micelles grow. On the other hand, micelles are dehydrated at higher temperatures resulting in decreased micellar hydration explaining the fall in micellar molar fraction and the micellar number density. 3.2. Rheology 10 ACS Paragon Plus Environment

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The influence of lavender oil on the flow behavior of P123 solutions and temperature induced gelation in the presence of ethanol was studied using steady and dynamic rheology of all the solutions studied by DLS. 3.2.1. Flow Curve To follow more on impact of added Lavender oil induced viscosity changes on P123 micelles in ethanol, flow tests were done on P123 micelles at different compositions and varying concentrations of ethanol in the systems of 5P+15E, 5P+20E, 5P+25E,10P+25E and 15P+25E. Solubilization of lavender oil in P123 micelles increases viscosity of the solution at higher oil compositions. The dependence of viscosity on shear for 5% P123 solution at various ethanol concentrations as a function of oil concentration (% v/v) (Fig. 5S in SI) reveal that all the solutions exhibit a non-Newtonian behavior, with shear thickening, shear thinning and finally a Newtonian behavior respectively at low, intermediate and higher shear rates. The viscosity increases only slightly with progressive addition of lavender oil, but a significant increase is observed above 0.99 %v/v of oil added for all the three systems (Fig. 5S). The results are in quite conformity with those obtained in DLS and SANS measurements where the bigger micelles predominated the solution of 5% P123 at around 1% v/v of added oil. Pluronic P123 at 5wt% in the presence of 15E, 20E and 25E at 1.32 and 1.64% v/v oil displays a clear soft gel phase, attributed to reversible entanglements between the corona of the neighboring micelles.61 The disruption of such entanglements results in shear thinning of the P123 micellar gel i due to applied shear which thereby largely reduces the viscosity of the system. The flow tests at higher P123 percentage (10P+25E) displayed similar behavior except for large values of viscosity. On the other hand, 15P+25E system revealed minimum variation of viscosity with shear rate upon the addition of Lavender oil (Fig. 6S). These results correlate fairly with the results of oil induced growth of P123 micelles obtained in DLS and SANS studies. 3.2.2. Gelation Temperature The oscillatory temperature tests were performed at low frequency (1 Hz), with heating rate set at 1 oC/min. Fig. 6 shows variation of storage modulus (G') for 5P+25E solutions with the addition of Lavender oil as function of temperature. . Upon heating the samples, an increase in modulus accompanied with transition from a sol state ( G" > G') to a viscoelastic state ( G' > G") is observed, with sol to soft-gel (Tg) transition marked at the point where G' increases sharply.47, 62 . As stated in the preceding section, the addition of oil favored micellization of P123 (CMT decreases) and 11 ACS Paragon Plus Environment

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therefore should assist in gelation as well, as the two phenomenon are codependent.63 Similar results were shown by solutions 5P+15E and 5P+20E (Fig. 7S). A sigmoid like dependence of G' on temperature is observed. The initial low G' values in first region are attributed to coexistence of O/W microemulsion droplets and P123 unimers. The region second observes sharp increase in G' within a small temperature range, taken sol-gel transition temperature (Tg).62 Such changes are connected to temperature favored conversion of unimers to P123 micelles on account dehydration of PPO in the core. Finally the onset of plateau in G' marks further aggregation of micelles into gels, analogous to the results reported for F127 based hydrogels in aqueous solution. 64 It is important to note that the point at which sharp increase in G' is observed shifts towards lower temperature scale while as the values of G' plateau increases in general with oil concentration. The gelation temperature (Tg) decreases almost linearly with increase in lavender oil concentration in all the systems of 5% P123 at various ethanol concentrations (Insets Fig. 6 and Fig 7S). As discussed previously, the addition of oil makes the system hydrophobic as the added oil causes dehydration of P123 micelles, increase in temperature dehydrates the micelles further and as a result the Tg decreases. At a fixed concentration of P123 (5%) and oil, Tg is also found to vary with ethanol concentration. It decreases from 46.8 to 31.3oC for 5P+10E, from 43.9 to 25.6 oC for 5P+15E and from 43.1 to 21.9 oC with the addition of Lavender oil from 0 to 1.64 (% v/v) respectively. The transition temperature was also found to vary with concentration of P123 as well. Fig. 7 depicts variation of G' for 10% and 15% P123 in the presence of 25% v/v ethanol at different oil concentrations with temperature. At higher concentration P123 gelation is pre-poned compared to other systems with lower concentration of P123, Tg decreases from 37.5 to 15.7oC for 10P+25E and from 28.2 to 9.6 oC for 15P+25E with increase in oil concentration from 0 to 3.23% v/v respectively. The temperature induced gelation in ethanolic P123 solutions has been studied previously and the phenomenon has been ascribed to transition of spherical micelles to elongated micelles and finally to worm like micelles before phase separation47. However, in the present case SANS did not reveal any sphere to rod transition ruling out the possibility of this mechanism. In our opinion and based on the DLS, SANS and Rheological measurements, we propose the following mechanism of temperature induced gelation (Scheme 2), motivated by other reports in the literature.65, 66 The P123 micelles exist as unimers below CMT. As the temperature is raised the micellization begins owing to dehydration of unimers because the supplied energy helps to dislodge the neighboring water.67 The micelles swell by the addition of lavender oil as explained in the preceding sections. 12 ACS Paragon Plus Environment

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The oil swollen micelles grow further upon heating that results in intermicellar entanglements of PEO blocks and higher friction. Thus, the possible viscoelastic behavior of ethanolic P123 in the presence of lavender oil can be explained in terms of balance between intermicellar entanglements of PEO blocks and intermicellar friction. If former exceeds, an elastic gel results (G' > G"), else a viscous solid (G' < G") is formed..65

4. Conclusions The lavender oil assisted aggregation characteristics of Pluronic P123 in ethanol-water mixed solvents provided valuable information regarding importance of P123/ethanol concentration for solubilizing a desired concentration of oil and role of the solubilizate in modulating the aggregation and rheological characteristics of the Pluronics. The structural evolution of the P123 solutions upon addition of the lavender oil reveals that relatively small amounts of added solubilizate has very pronounced effect on the P123 micelles by rendering it more hydrophobic, improving aggregation characteristics and lowering gelation temperature. Through the microstructural study it turned out that P123 systems are able to solubilize high amounts of lavender oil. It is presumed that the extent of oil penetration and nature of copolymer self-assembly can be of immense use in slowing down the evaporation rate of volatiles which we desire to smell over a longer period of time. The perceptions added afford a significant development in the understanding of the influence of essential oils on copolymer self-assembly, to be kept in mind while designing effective copolymer based formulations.


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References 1. Khan, I. A.; Abourashed, E. A. Leung's Encyclopedia of Common Natural Ingredients: Used in Food, Drugs and Cosmetics; Wiley2011. 2. Reverchon, E.; Porta, G. D.; Senatore, F. Supercritical CO2 Extraction and Fractionation of Lavender Essential Oil and Waxes. J. Agric. Food. Chem. 1995, 43 (6), 1654-1658. 3. De Haas, C. Lavender, the most essential oil : recipes for pampering, good health, nurturing and well-being- naturally; Pennon Publishing: Essendon North, Vic., 2001. 4. Gülçin, Ì.; Güngör Şat, İ.; Beydemir, Ş.; Elmastaş, M.; İrfan Küfrevioǧlu, Ö. Comparison of antioxidant activity of clove (Eugenia caryophylata Thunb) buds and lavender (Lavandula stoechas L.). Food Chem. 2004, 87 (3), 393-400. 5. Topal, U.; Sasaki, M.; Goto, M.; Otles, S. Chemical compositions and antioxidant properties of essential oils from nine species of Turkish plants obtained by supercritical carbon dioxide extraction and steam distillation. International Journal of Food Sciences and Nutrition 2008, 59 (7-8), 619-634. 6. Lu Hui, L. H., Lu Huan, Li XiaoLan and Zhou AiGuo. Chemical composition of lavender essential oil and its antioxidant activity and inhibition against rhinitis-related bacteria. African Journal of Microbiology Research 2010, 4 (4), 309-313. 7. Kim, N.-S.; Lee, D.-S. Comparison of different extraction methods for the analysis of fragrances from Lavandula species by gas chromatography–mass spectrometry. J. Chromatogr. A 2002, 982 (1), 31-47. 8. Catherine J. Chu and Kathi J. Kemper, M., MPH. Lavender (Lavandula spp.). Longwood Herbal Task Force 2001, 1-32. 9. Palá-Paúl, J.; Brophy, J. J.; Goldsack, R. J.; Fontaniella, B. Analysis of the volatile components of Lavandula canariensis (L.) Mill., a Canary Islands endemic species, growing in Australia. Biochem. Syst. Ecol. 2004, 32 (1), 55-62. 10. Friberg, S. E. Fragrance compounds and amphiphilic association structures. Adv. Colloid Interface Sci. 1998, 75 (3), 181-214. 11. Aikens, P.; Friberg, S. E. Organized assemblies in cosmetics and transdermal drug delivery. Current Opinion in Colloid & Interface Science 1996, 1 (5), 672-676. 12. Milotic, D. The impact of fragrance on consumer choice. Journal of Consumer Behaviour 2003, 3 (2), 179-191. 13. Magdassi, S. Delivery systems in cosmetics. Colloids and Surfaces A: Physicochemical and Engineering Aspects 1997, 123 (Supplement C), 671-679. 14. Andersson Trojer, M.; Nordstierna, L.; Nordin, M.; Nyden, M.; Holmberg, K. Encapsulation of actives for sustained release. PCCP 2013, 15 (41), 17727-17741. 15. Given, P. S. Encapsulation of Flavors in Emulsions for Beverages. Current Opinion in Colloid & Interface Science 2009, 14 (1), 43-47. 16. Petrovic, L. B.; Sovilj, V. J.; Katona, J. M.; Milanovic, J. L. Influence of polymer– surfactant interactions on o/w emulsion properties and microcapsule formation. J. Colloid Interface Sci. 2010, 342 (2), 333-339. 17. Berthier, D.; Paret, N.; Trachsel, A.; Fieber, W.; Herrmann, A. Controlled Release of Damascone from Poly(styrene-co-maleic anhydride)-based Bioconjugates in Functional Perfumery. Polymers 2013, 5 (1), 234. 14 ACS Paragon Plus Environment

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18. Bradbury, R.; Penfold, J.; Thomas, R. K.; Tucker, I. M.; Petkov, J. T.; Jones, C. Enhanced perfume surface delivery to interfaces using surfactant surface multilayer structures. J. Colloid Interface Sci. 2016, 461 (Supplement C), 352-358. 19. Bradbury, R.; Penfold, J.; Thomas, R. K.; Tucker, I. M.; Petkov, J. T.; Jones, C. Manipulating perfume delivery to the interface using polymer–surfactant interactions. J. Colloid Interface Sci. 2016, 466 (Supplement C), 220-226. 20. Edris, A. E.; Malone, C. F. R. Preferential solubilization behaviours and stability of some phenolic-bearing essential oils formulated in different microemulsion systems. International Journal of Cosmetic Science 2012, 34 (5), 441-450. 21. Tokuoka, Y.; Uchiyama, H.; Abe, M.; Ogino, K. Solubilization of synthetic perfumes by nonionic surfactants. J. Colloid Interface Sci. 1992, 152 (2), 402-409. 22. Tokuoka, Y.; Uchiyama, H.; Abe, M. Solubilization of Some Synthetic Perfumes by Anionic-Nonionic Mixed Surfactant Systems. 2. The Journal of Physical Chemistry 1994, 98 (24), 6167-6171. 23. Tokuoka, Y.; Uchiyama, H.; Abe, M.; Christian, S. D. Solubilization of Some Synthetic Perfumes by Anionic-Nonionic Mixed Surfactant Systems. 1. Langmuir 1995, 11 (3), 725-729. 24. Abe, M.; Mizuguchi, K.; Kondo, Y.; Ogino, K.; Uchiyama, H.; Scamehorn, J. F.; Tucker, E. E.; Christian, S. D. Solubilization of Perfume Compounds by Pure and Mixtures of Surfactants. J. Colloid Interface Sci. 1993, 160 (1), 16-23. 25. Yang, J.; Rong, G. U. O.; Friberg, S. E.; Aikens, P. A. The phase behaviour of polyoxyethylene 10 stearyl ether/geraniol/olive oil/H2O system and preliminary evaluation of fragrance evaporation. International Journal of Cosmetic Science 1996, 18 (2), 43-56. 26. Kondo, Y.; Abe, M.; Ogino, K.; Uchiyama, H.; Scamehorn, J. F.; Tucker, E. E.; Christian, S. D. Solubilization of 2-phenylethanol in surfactant vesicles and micelles. Langmuir 1993, 9 (4), 899-902. 27. Kayali, I.; Khan, A.; Lindman, B. Solubilization and location of phenethylalcohol, benzaldehyde, and limonene in lamellar liquid crystal formed with block copolymer and water. J. Colloid Interface Sci. 2006, 297 (2), 792-796. 28. S.E. Friberg, J. Y. Solubilization in Cosmetic Systems. Surfactant in Cosmetic. In Surfactant in Cosmetic, M.M. Rieger, L. R., Ed.; Dekker: New York, 1997; Vol. 68, p 225. 29. Bradbury, R.; Penfold, J.; Thomas, R. K.; Tucker, I. M.; Petkov, J. T.; Jones, C. Adsorption of Model Perfumes at the Air–Solution Interface by Coadsorption with an Anionic Surfactant. Langmuir 2013, 29 (10), 3361-3369. 30. Bradbury, R.; Penfold, J.; Thomas, R. K.; Tucker, I. M.; Petkov, J. T.; Jones, C. The impact of alkyl sulfate surfactant geometry and electrolyte on the co-adsorption of anionic surfactants with model perfumes at the air–solution interface. J. Colloid Interface Sci. 2013, 403 (Supplement C), 84-90. 31. Penfold, J.; Staples, E.; Tucker, I.; Soubiran, L.; Thomas, R. K. Comparison of the Coadsorption of Benzyl Alcohol and Phenyl Ethanol with the Cationic Surfactant, Hexadecyl Trimethyl Ammonium Bromide, at the Air–Water Interface. J. Colloid Interface Sci. 2002, 247 (2), 397-403. 32. Penfold, J.; Thomas, R. K.; Bradbury, R.; Tucker, I.; Petkov, J. T.; Jones, C. W.; Webster, J. R. P. Probing the surface of aqueous surfactant-perfume mixed solutions during perfume evaporation. Colloids and Surfaces A: Physicochemical and Engineering Aspects 2017, 520 (Supplement C), 178-183.


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33. Suzuki, K.; Saito, Y.; Tokuoka, Y.; Abe, M.; Sato, T. Poly(ethylene oxide)/poly(propylene oxide)/poly(ethylene oxide) triblock copolymer as a sustained-release carrier for perfume compounds. J Amer Oil Chem Soc 1997, 74 (1), 55-59. 34. Friberg, S. E. Vapour pressure of some fragrance ingredients in emulsion and microemulsion formulations. Int J Cosmet Sci 1997, 19 (2), 75-86. 35. Friberg, S. E.; Szymula, M.; Fei, L.; Barber, J.; Al-Bawab, A.; Aikens, P. A. Vapour pressure of a fragrance ingredient during evaporation in a simple emulsion. International Journal of Cosmetic Science 1997, 19 (6), 259-270. 36. Friberg, S. E.; Yin, Q.; Aikens, P. A. Vapour pressures of phenethyl alcohol and limonene in systems with water and Laureth 4. International Journal of Cosmetic Science 1998, 20 (6), 355-367. 37. Fei, L.; Szymula, M.; Friberg, S. E.; Aikens, P. A. Vapor pressure of phenethyl alocohol and phenethyl acetate in the system with water and nonionic surfactant — Polyoxyethylene 4 lauryl ether (Brij®30). In Structure, Dynamics and Properties of Disperse Colloidal Systems, Rehage, H.; Peschel, G., Eds.; Steinkopff: Darmstadt, 1998, pp 85-91. 38. Friberg, S. E.; Yin, Q.; Aikens, P. A. Vapor pressures and amphiphilic association structures. Colloids and Surfaces A: Physicochemical and Engineering Aspects 1999, 159 (1), 17-30. 39. Berthier, D. L.; Schmidt, I.; Fieber, W.; Schatz, C.; Furrer, A.; Wong, K.; Lecommandoux, S. b. Controlled Release of Volatile Fragrance Molecules from PEO-b-PPO-bPEO Block Copolymer Micelles in Ethanol−Water Mixtures. Langmuir 2010, 26 (11), 79537961. 40. Saito∗, Y.; Miura, K.; Tokuoka, Y.; Kondo, Y.; Abe, M.; Sato, T. VOLATILITY AND SOLUBILIZATION OF SYNTHETIC FRAGRANCES BY PLURONIC P-85. J. Dispersion Sci. Technol. 1996, 17 (6), 567-576. 41. Zhang, Z.; Barber, J. L.; Friberg, S. E.; Aikens, P. A. FRAGRANCE EMULSIONS STABILIZED BY A TRIBLOCK COPOLYMER. J. Dispersion Sci. Technol. 2000, 21 (2), 145160. 42. Lavasanifar, A.; Samuel, J.; Kwon, G. S. Poly(ethylene oxide)-block-poly(l-amino acid) micelles for drug delivery. Advanced Drug Delivery Reviews 2002, 54 (2), 169-190. 43. Rodríguez-Hernández, J.; Chécot, F.; Gnanou, Y.; Lecommandoux, S. Toward ‘smart’ nano-objects by self-assembly of block copolymers in solution. Prog. Polym. Sci. 2005, 30 (7), 691-724. 44. Schmolka, I. R. A review of block polymer surfactants. Journal of the American Oil Chemists’ Society 1977, 54 (3), 110-116. 45. Saito, Y.; Miura, K.; Tokuoka, Y.; Kondo, Y.; Abe, M.; Sato, T. VOLATILITY AND SOLUBILIZATION OF SYNTHETIC FRAGRANCES BY PLURONIC P-85. J. Dispersion Sci. Technol. 1996, 17 (6), 567-576. 46. Kayali, I. Solubilization of fragrance compounds in block copolymer/water system. Jordan J. Appl. Sci., Nat. Sci. 2003, 5 (2), 42-49. 47. Chaibundit, C.; Ricardo, N. M. P. S.; Ricardo, N. M. P. S.; Costa, F. d. M. L. L.; Wong, M. G. P.; Hermida-Merino, D.; Rodriguez-Perez, J.; Hamley, I. W.; Yeates, S. G.; Booth, C. Effect of Ethanol on the Micellization and Gelation of Pluronic P123. Langmuir 2008, 24 (21), 12260-12266. 48. Alexandridis, P.; Yang, L. SANS Investigation of Polyether Block Copolymer Micelle Structure in Mixed Solvents of Water and Formamide, Ethanol, or Glycerol. Macromolecules 2000, 33 (15), 5574-5587. 16 ACS Paragon Plus Environment

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Figure Captions Figure 1.(a) Variation in the correlation function diagram of 5% P123+15% v/v ethanol with increasing Lavender oil (v/v) concentration recorded at o a scattering angle of 130 o. The solid lines represent fit to the data based on Cumulant analysis and (b) The corresponding intensityweighted size distribution plots. Figure 2. Comparative size variation of 5% P123 with the addition of Lavender oil in the presence of different Ethanol concentrations. Figure 3. SANS patterns of P123 in the presence of ethanol at varying Lavender oil (% v/v) concentrations (a) 5% P123+ 15% Ethanol (b)5% P123+ 25% Ethanol . The solid lines are fit to the data. Figure 4. SANS patterns of 15% P123+ 25% Ethanol at varying concentrations of Lavender oil. The solid lines are fit to the data. Figure 5. SANS patterns of P123 at two different temperatures 15% P123+ 25% Ethanol. The solid lines are fit to the data. Figure 6. Variation of Storage Modulus (G') as a function of temperature for: 5P+25E at various oil (% v/v) concentrations. Inset depicts variation of sol-gel transition temperature (Tg) with Lavender oil (% v/v) concentration. Figure 7. Storage Modulus as a function of temperature: (a) 10P+25E and (b)15P+25E. Inset depicts variation of sol-gel transition temperature (Tg) with Lavender oil concentration. Scheme 1. Schematic representation of Lavender oil solubilization by P123 micelles. Scheme 2. Schematic representation of proposed P123 gelation mechanism with temperature in the presence of Lavender oil.


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Table 1. Micellar parameters viz. core radius (RC), polydispersity (), hard sphere radius (RHS), aggregation number (N), micellar volume fraction () and number density of micelles per cc(n) for different P123 Solutions at various Lavender oil concentrations in the presence of different ethanol concentrations at 30 oC . % v/v

RC (nm)

0.00 0.66 0.99 1.32

5.39 6.24 6.51 6.70

0.00 0.66 0.99 1.32

4.83 5.60 5.87 6.24

0.00 1.32 2.60 3.23

4.41 4.81 5.15 5.38

RHS (nm) N  (a) 5 % P123 + 15 % Ethanol (5P+15E) 0.23 8.32 98.3 0.28 8.95 152.5 0.31 9.40 173.1 0.35 9.75 188.7 (b) 5 % P123 + 25 % Ethanol (5P+25E) 0.23 7.88 70.7 0.25 8.62 110.2 0.27 8.95 126.9 0.31 9.40 152.5 (c) 15 % P123 + 25 % Ethanol (15P+25E) 0.19 6.76 53.8 0.21 7.54 69.8 0.23 7.86 85.7 0.25 8.35 97.7



n

0.072 0.068 0.062 0.06

2.98332E+16 2.26348E+16 1.78133E+16 1.54481E+16

0.081 0.079 0.075 0.07

3.95042E+16 2.94335E+16 2.49648E+16 2.01118E+16

0.24 0.23 0.2 0.18

1.85399E+17 1.28041E+17 9.82877E+16 7.37819E+16


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Table 2. Effect of temperature on P123 micellar parameters viz. core radius (RC), polydispersity (), hard sphere radius (RHS), aggregation number (N), micellar volume fraction () and number density of micelles (n)at various Lavender oil concentrations in the presence of different ethanol concentrations. T (oC)

RC (nm)

0.00 0.00 1.32 1.32

30 50 30 50

5.39 5.98 6.70 7.05

0.00 0.00 1.32 1.32

30 50 30 50

4.83 5.34 6.24 6.45

0.00 0.00 2.60 2.60

30 50 30 50

4.41 4.80 5.15 5.44

% v/v

RHS (nm)  (a) 5 % P123 + 15 % Ethanol 0.23 8.32 0.3 9.0 0.35 9.75 0.4 10.2 (b) 5 % P123 + 25 % Ethanol 0.23 7.88 0.24 8.30 0.31 9.40 0.35 9.90 (c) 15 % P123 + 25 % Ethanol 0.19 6.76 0.22 7.38 0.23 7.86 0.25 8.48





n

98.3 134.2 188.7 219.9

0.072 0.065 0.06 0.055

2.98332E+16 2.12776E+16 1.54481E+16 1.2368E+16

70.7 95.6 152.5 168.4

0.081 0.068 0.07 0.06

3.95042E+16 2.83799E+16 2.01118E+16 1.47565E+16

53.8 69.4 85.7 101.0

0.24 0.2 0.2 0.17

1.85399E+17 1.1874E+17 9.82877E+16 6.6527E+16


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10

100

1000

15 10

0.0 v/v oil 0.66 1.32

(a)

1.0

1.32

(b)

5 0 15

0.8

0.99

10 5

Intensity

0.6

g1()

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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0.4 0.2

0 15

0.66

10 5 0 15

0.33

10 5

0.0

0 15

1

10

100

Time (S)

1000

10000

0 % v/v Oil

10 5 0

10

100

1000

2R (nm) h

Figure 1.(a) Variation in the correlation function diagram of 5% P123+15% v/v ethanol with increasing Lavender oil (v/v) concentration recorded at a scattering angle of 130 o. The solid lines represent fit to the data based on Cumulant analysis and (b) The corresponding intensityweighted size distribution plots. The experiments were carried at 30 oC.


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140

5P+15E 5P+20E 5P+25E

120 100

Size (nm)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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80 60 40 20 0 0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Lavender Oil (vol. %)

Figure 2. Comparative size variation of 5% P123 with the addition of Lavender oil in the presence of different Ethanol concentrations. The experiments were carried at 30 oC.


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90 (b) 5 % P123 + 25 % Ethanol

(a) 5 % P123 + 15 % Ethanol 0.0 % v/v oil 0.66 0.99 1.32

90 60

0.0 % v/v oil 0.66 0.99 1.32

d/d (cm-1)

120

d/d (cm-1)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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60

30

30 0

0.015

0

0.04 Q (Å-1)

0.08 0.4

0.015 0.02

0.04 Q (Å-1)

0.06 0.08 0.4

Figure 3. SANS patterns of P123 in the presence of ethanol at varying Lavender oil (% v/v) concentrations (a) 5% P123+ 15% Ethanol (b)5% P123+ 25% Ethanol at 30 oC. The solid lines are fit to the data.


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90

d/d (cm-1)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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60

15 % P123 + 25 % Ethanol 0.0 % v/v Oil 1.32 2.60 3.23

30

0

0.015 0.02

0.04

0.06 0.08 0.4

-1

Q (Å ) Figure 4. SANS patterns of 15% P123+ 25% Ethanol at varying concentrations of Lavender oil at 30 oC. The solid lines are fit to the data.


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d/d (cm-1)

150 120 90 60

(a) 5 % P123 + 15 % Ethanol % v/v Oil o 0.0 at 30 C o 0.0 at 50 C o 1.32 at 30 C o 1.32 at 50 C

30 0

d/d (cm-1)

(b) 5 % P123 + 25 % Ethanol

80 60 40

% v/v Oil o 0.0 at 30 C o 0.0 at 50 C o 1.32 at 30 C o 1.32 at 50 C

20 0 90

d/d (cm-1)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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(c) 15 % P123 + 25 % Ethanol % v/v Oil o 0.0 at 30 C o 0.0 at 50 C o 2.60 at 30 C o 2.60 at 50 C

60 30 0 0.015

0.04 -1

0.08 0.4

Q (Å )

Figure 5. SANS patterns of P123 at two different temperatures for (a) 5% P123+ 15% Ethanol (b)5% P123+ 25% Ethanol and (c)15% P123+ 25% Ethanol. The solid lines are fit to the data.


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45

10

Tg (oC)

40

Storage Modulus (Pa)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

35 30 25

1

0.1

20 0.0

0.5

0% v/v Oil 0.66 1.32 1.96

1.0

Oil (L)

1.5

2.0

0.01

10

20 30 40 50 60 Temperature (oC)

Figure 6. Variation of Storage Modulus (G') as a function of temperature for 5P+25E at various oil (% v/v) concentrations. Inset depicts variation of sol-gel transition temperature (Tg) with Lavender oil (% v/v) concentration.


Langmuir

30

100

35

10

25

20

Tg (oC)

30

15

10

20

10 0

15

1

25

o

40

Tg ( C)

100

Storage Modulus (Pa)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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0

1

2

2

3

3

Oil (% v/v)

0.0 % v/v Oil 1.32 2.60 3.23

0.1

1

Oil (% v/v)

1

0.0 % v/v Oil 1.32 2.60 3.23

0.1

(a)

15

25 35 45 55 Temperature (oC)

(b)

15

25

35

45

Temperature (oC)

Figure 7. Storage Modulus as a function of temperature: (a) 10P+25E and (b)15P+25E. Inset depicts variation of sol-gel transition temperature (Tg) with Lavender oil concentration.


55

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Scheme 1. Schematic representation of Lavender oil solubilization by P123 micelles.

Scheme 2. Schematic representation of proposed P123 gelation mechanism with temperature in the presence of Lavender oil.


Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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TOC Graphics


Aggregation and Rheological Behavior of the ... - ACS Publications

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