Colloids and Surfaces A: Physicochem. Eng. Aspects 431 (2013) 93–104 Contents lists available at SciVerse ScienceDirect Colloids and Surfaces A: Physicochemical and Engineering Aspects jo ur nal ho me page: www.elsevier.com/locate/colsurfa Variable temperature multiple light scattering analysis to determine the enthalpic term of a reversible agglomeration in submicrometric colloidal formulations: A quick quantitative comparison of the relative physical stability Luana A. Fiel a , Márcia D. Adorne b , Sílvia S. Guterres a,c , Paulo A. Netz d,∗∗ , Adriana R. Pohlmann a,b,c,∗ a Pós-Graduac ¸ ão em Ciências Farmacêuticas, Faculdade de Farmácia, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil b Departamento de Química Orgânica, Instituto de Química, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil c Centro de Nanociência e Nanotecnologia, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil d Departamento de Físico-Química, Instituto de Química, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil h i g h l i g h t s • Stability rank of liquid colloidal dis- persions was assessed by a new approach. • The VTMLS approach was used to compare the physical stability of nanocapsules. • The agglomeration process was quantitatively estimated. • The reversible agglomeration was resolved from the irreversible aggre- gation. • The new approach is a non- destructive method. g r a p h i c a l a b s t r a c t The quantitative relative stability of the submicrometric particles was assessed by determining the values of an enthalpic term (A ′ H ◦ ) involved in the agglomeration process. The higher are the A ′ H ◦ values, the lower is the physical stability of the formulations. a r t i c l e i n f o Article history: Received 22 February 2013 Received in revised form 4 April 2013 Accepted 10 April 2013 Available online 24 April 2013 Keywords: Nanocapsules Multiple light scattering a b s t r a c t In this work, we propose the variable temperature multiple light scattering (VTMLS) as a novel method to determine an enthalpic term of the agglomeration process of submicrometric colloidal systems such as polymeric nanocapsules (NCs) and lipid-core nanocapsules (LNCs). Four different aqueous suspensions were prepared using a linear polyester, triacylglycerol, octyl methoxycinnamate and polysorbate 80 in the presence (individually and combined) or absence of the surfactants: phosphatidylcholine and sorbitan monostearate. Backscattering (BS) signals were monitored applying a temperature gradient from 23 ◦ C to 56 ◦ C (increase of 3 ◦ C at 5-min intervals). Considering the Indefinite Self-Association Model, a relation between the BS signal and the equilibrium constant of the agglomeration process was established. Abbreviations: A ′ , positive proportionality constant; , particle volume fraction; ˚ ′ , osmotic coefficient; BS, backscattering; CCT, caprylic/capric triglyceride; CN, total agglomerate concentration; CO, clove oil; CT, total concentration of the original particles; d, particle size of the dispersed phase; D [4,3] , volume-weighted mean diameters; DSC, Differential scanning calorimetry; g, asymmetry factor; K, equilibrium constant; ℓ*, photon transport length in the medium; LNCs, lipid-core nanocapsules; NCs, nanocapsules; NE, nanoemulsion; OMC, octyl methoxycinnamate; P, particles; PC, phosphatidylcholine; PCS, photon correlation spectroscopy; PDI, polydispersity indexes; Pn, agglomerates; Qs, scattering efficiency factor; SAXS, Small-angle X-ray scattering; SPAN, polydispersity; T, temperature; VTMLS, variable temperature multiple light scattering; G ◦ , standard Gibbs energy change; H ◦ , enthalpy changes under standard conditions; S ◦ , entropy changes under standard conditions. ∗ Corresponding author at: Departamento de Química Orgânica, Instituto de Química, Universidade Federal do Rio Grande do Sul, Av. Bento Gonc ¸ alves, 9500, PBox 15003, CEP 91501-970 Porto Alegre, RS, Brazil. Tel.: +55 51 33087237; fax: +55 51 33087304. ∗∗ Corresponding author at: Departamento de Físico-Química, Instituto de Química, Universidade Federal do Rio Grande do Sul, Av. Bento Gonc ¸ alves, 9500, Agronomia, CEP 91501-970 Porto Alegre, RS, Brazil. Tel.: +55 51 33086276; fax: +55 51 33087304. E-mail addresses: netz@iq.ufrgs.br (P.A. Netz), adriana.pohlmann@ufrgs.br, pohlmann@iq.ufrgs.br (A.R. Pohlmann). 0927-7757/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.colsurfa.2013.04.015