Hindawi Publishing Corporation Journal of Chemistry Volume 2013, Article ID 938042, 7 pages http://dx.doi.org/10.1155/2013/938042 Research Article Assessment of Physical Stability and Antioxidant Activity of Polysiloxane Polyalkyl Polyether Copolymer-Based Creams Atif Ali, Naveed Akhtar, and Haji Muhammad Shoaib Khan Faculty of Pharmacy and Alternative Medicines, e Islamia University of Bahawalpur, Bahawalpur 63100, Pakistan Correspondence should be addressed to Atif Ali; ajmaline2000@gmail.com Received 5 March 2012; Revised 7 May 2012; Accepted 8 May 2012 Academic Editor: Ana B. Martin-Diana Copyright © 2013 Atif Ali et al. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. e purpose of the present work was to investigate the changes on physical stability (color, creaming, liquefaction, pH, conductivity, centrifugation, viscosity and rheological parameters) by non-ionic surfactant polysiloxane polyalkyl polyether copolymer based creams following inclusion of plant extract containing phenolic compounds. e antioxidant activity of the plant extract alone and aer addition in the cream was assessed using the stable free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay. Physical stability was assessed by submitting the creams to storage at 8 ∘ C, 25 ∘ C, 40 ∘ C, and at 40 ∘ C with 70% RH (relative humidity) for a period of two months. Physical characteristics of polysiloxane polyalkyl polyether copolymer based creams, that is, color, creaming, liquefaction, centrifugation and pH were noted at various intervals for 2 months. e viscosities and rheological behavior of creams were determined using a rotational rheometer. Data were analyzed by using Brook�eld �oware Rheocalc version (2.6) with IPC Paste and Power Law (PL) math models. Cream with plant extract showed pseudo plastic behaviour with decreasing on viscosity. e Acacia nilotica (AN) extract alone and the cream containing this extract showed great antioxidant and free radical scavenging activities. Power Law and IPC analysis were found to �t all the rheograms. 1. Introduction Plants produce a number of antioxidants against molec- ular damage from reactive oxygen species, and phenolic antioxidants are one of the major classes which act as photoprotectives [1]. In the recent years phenolics have gained considerable attention due to their use in skin care, such as dryness, eczema, acne, free radical scavenging, anti- in�ammatory, anti-aging, and skin protection e�ects [2]. Phenolics act as antioxidants in a number of ways [1] by formation of long-lived radical results, hydrogen donating phenolics and reactive oxygen species are able to modify the radical-mediated oxidation processes [2], by chelating metal ions with phenolics involved in the production of free radicals [3] and by inhibiting enzymes such as various cytochrome P450 isoforms, lipoxygenases, cyclooxygenase, and xanthine oxidase involved in radical formations [3]. Polysiloxane polyalkyl polyether copolymer (ABIL EM 90) is a nonionic surfactant [4] with outstanding heat and freeze/thaw stability. It is oil soluble, and its HLB value is 5. It is used as emulsi�er for sun shield preparations with high content of organic and/or physical �V �lters. It has high compatibility with active ingredients. It makes possible a dispersion of aqueous droplets within an oil phase [5]. Researchers have reported the antioxidant activity in vitro or in vivo of Acacia nilotica extract [6, 7]. Acacia nilotica extract has antioxidant activity against hydroxyl, superoxide, and peroxyl radicals [8] and thus may play a role in the treatment of diseases involving free radicals and oxidative damage [9] such as cancer and aging. Incorporation of antioxidants and phenolic compounds topically has recently proved to symbolize a �ourishing strategy for protecting the skin against oxidative damage [10], but there is no data in text in the best of our knowledge about their efficacy in topical preparations of Acacia nilotica extract and their in�uence on physical stability of the formulation. Copious rheological studies have been conducted on emulsions [11]. Rheological properties can be divided into viscous, elastic, and plastic properties and combinations of these, viscoelasticity being the most important for semisolids.