Surfactant Science: Principles and Practice Prof Steven Abbott
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Surfactant Science: Principles and Practice Prof Steven Abbott Steven Abbott TCNF Ltd, Ipswich, UK and Visiting Professor, University of Leeds, UK [email protected] www.stevenabbott.co.uk Version history: 1.0.0 20 September 2015 Initial release 1.0.1 23 September 2015 Addition of surfactant solubilizers 1.0.2 26 January 2016 Minor mods 1.0.3 07 March 2016 Update to new website and Fast Scans 1.0.4 03 October 2018 Update on NAC calculations plus minor mods 1.0.5 28 November 2019 Update with the new Acosta Polar Oil approach 1.0.6 20 January 2019 Update on foam making Copyright © 2015/20 Steven Abbott This book is distributed under the Creative Commons BY-ND, Attribution and No-Derivatives license. Contents Preface 6 Abbreviations and Symbols 12 1 Some Basics 13 1.1 A summary in 9 images 13 1.2 What’s not included 14 1.3 CMC, Γm, A, K, E. Who cares? 15 1.4 Why CPP is mostly useless 22 1.5 Bancroft’s “Rule” 25 1.6 Why HLB should be banned 27 1.7 Surfactant blends 29 1.8 Elasticity and bending 30 1.9 Cloud Point and Krafft Point 33 1.10 Dynamic Surface Tension 36 1.10.1 Classic DST 36 1.10.2 DST around equilibrium 42 1.11 Partition coefficient 45 1.11.1 Measuring partition coefficients 46 1.12 The basics summarised 47 2 HLD – towards rational emulsions 49 2.1 Specific HLD examples 50 2.2 A waste of good surfactant 54 2.3 Extended Oil Recovery, EOR 55 2.4 Measuring Cc and EACN 57 2.4.1 Scan tricks 60 2.4.2 Phase volumes 61 2.4.3 Fast scans 61 2.4.4 Silicone oils 64 2.5 Winsor R ratio and Packing Parameter 64 2.6 Who cares about microemulsions? 67 2.7 HLD is not enough 68 3 NAC – Net Average Curvature 70 3.1 What can NAC do? 72 3.2 More fish power from NAC 78 3.3 More power from NAC – the fishtail plot 81 3.4 PIF – Phase Inversion Formulation 83 3.5 Going on for ever 84 3.6 The problem of ξ 86 3.6.1 Phase volumes 88 3.6.2 Other ways to look at ξ 91 3.6.3 Creating a large ξ for efficiency 91 3.6.4 CµC 92 3.6.5 Silicone oils 93 3.7 The point of this chapter 93 4 Emulsions 96 4.1 The numbers behind an emulsion 96 4.2 Size distributions 97 4.3 Viscosity 99 4.4 Avoiding destruction 101 4.4.1 Creaming 101 4.4.2 Ostwald Ripening 102 4.4.3 Flocculation 105 4.4.4 Coalescence 109 4.4.5 DLVO 111 4.4.6 Dynamic barriers: Elasticity, Gibbs-Marangoni and Wedges 114 4.5 How to make an emulsion 117 4.5.1 How not to make an emulsion 118 4.5.2 Predicting drop size 120 4.5.3 Using HLD-NAC 123 4.6 Emulsions by Catastrophic Inversion 126 4.7 Pickering emulsions 133 5 Foams 136 5.1 Foam basics 137 5.2 Elasticity 138 5.3 Foam DLVO 141 5.4 Ostwald ripening 144 5.5 Foam Drainage 148 5.6 Foam Rheology 153 5.7 Antifoams 157 5.7.1 Practical issues 158 5.7.2 3 Coefficients 159 5.7.3 The Entry Barrier problem 161 5.7.4 Fast and slow 163 5.7.5 Disappearing antifoam 164 5.7.6 Now for the science bit 165 5.8 Making foams 168 5.8.1 Foam making essentials 168 5.8.2 But what about my surfactant system? 171 5.8.3 The view from 2020 171 5.8.4 Foaming techniques 173 5.8.5 Measurements of key parameters. 174 5.9 Foam fractionation 175 6 Problems 180 6.1 The polar oil problem 180 6.2 Building on the CIT model 183 6.3 Polar oils as surfactants and oils 186 6.4 Linkers, hydrotropes etc. 189 6.5 From problem to opportunity 192 6.5.1 Γm, A, K and elasticity 193 6.5.2 Curvature and IFT 194 6.5.3 Together 195 7 Phase diagrams 197 7.1 Phases 197 7.2 Binary diagrams 201 7.3 Ternary diagrams 203 7.3.1 Reading values from a ternary diagram 203 7.3.2 Paths through phase diagrams 207 7.3.3 Diagrams with 2-phase regions 208 7.3.4 Diagrams with 3-phase regions 209 7.3.5 HLD-NAC and microemulsion diagrams 211 7.3.6 General ternary diagrams 212 8 Putting the principles into practice 214 8.1 Detergency 214 8.2 EOR 224 8.2.1 Soil remediation 227 8.2.2 Dealing with oil spills 228 8.3 Cosmetics emulsions 229 8.4 Emulsion Polymerisation 234 8.5 Making inorganic nanoparticles 240 8.6 Emulsion Separation 242 8.7 Bicontinuous Microemulsions 244 8.7.1 Microemulsion solvent cleaners 244 8.7.2 Cosmetic microemulsions 246 8.8 Levelling of paints and coatings 248 8.8.1 Surfactants to fix pinholes 249 8.8.2 Surfactants to fix other levelling issues 250 8.9 High throughput 252 8.9.1 Phase scans for Cc, EACN etc. 252 8.9.2 Phase diagrams 253 8.9.3 Small volume tricks 254 8.10 Surfactants as Solubilizers 257 8.11 The future of surfactant formulation practice 260 Preface The target audience for this book is a younger version of myself. I have included all those things I wish I had known years ago. Had I had this book, my life of formulating with surfactants would have been so much more productive! This book, therefore, contains everything that I know about surfactant science that can be useful to someone (such as myself) who formulates with surfactants. So it is a good idea to make it clear right from the start that although there are many good answers to many of our formulation questions (and these answers generally are not the ones you read about) there are lots of surfactant questions for which surfactant science currently has no satisfactory answers. As we will see, I am happy to blame the surfactant community for having wasted decades by not working with the best available surfactant theory, and therefore not having the time or the clarity to investigate the extra questions for which formulators really wanted answers. More specifically I lay the blame on those in academia and industry who perpetuated the myth that armed with critical micelle concentration, CMC, and with hydrophilic lipophilic balance, HLB, one could formulate wisely. As countless formulators have found, these, the only numbers that are generally mentioned in the surfactant literature, are largely useless for most purposes. Those who formulate exclusively with ethoxylates will take some exception to this. Because ethoxylates can be formulated with any combination of alkane and ethoxylate chain lengths there have been endless studies and correlations from which a formulator can derive some useful answers armed only with the CMC and HLB values. Ethoxylates, however, are a good part of the larger problem because their somewhat rational behaviour has been used as a cover to pretend that the rest of surfactant science can use ethoxylate- based techniques. This is simply untrue. Outside the world of ethoxylates, HLB is largely meaningless and valueless. And few of us can take long lists of CMC values and reach deep insights into our formulation problems. The good news is that once you exit the world of HLB there are a set of scientific principles (especially HLD) on which to build a much more solid base for formulations. In some areas the formulations can be entirely rational. In other areas we at least know which bits of science are lacking so the formulator can tell how far to push the science before relying on whatever other resources lie to hand. I always found surfactant science hard, and regularly skipped over stuff I thought was useless or irrelevant. My aim in this book is to give you the science you really must know, and give it in the easiest-possible manner. That means a book/app hybrid. Every key equation in the book is linked to an app that brings the equation to life. Because this is an eBook-only publication, readers simply have to click on the link in whatever eBook Reader they are using (e.g. iBooks, Kindle, Acrobat pdf) and the app will open in their default web browser, ready for immediate exploration. The inputs are invariably via sliders. Those on PCs and Macs might prefer inputs via text boxes. Those on tablets and phones would hate text inputs – they simply aren’t practical when (as is often the case) there are multiple inputs to be provided. What topics should be included? I am still amazed by the way that “useless” knowledge from one subject area turns out to be useful in another area. I have therefore included chapters on any area where I happened to find some useful surfactant science. Even if you have no interest in, say, foams or emulsion polymerisation there is still a lot to learn that might well apply to your own area of interest. Although, for example, it might be obvious to foam scientists that scientifically a foam is very much the same as an emulsion, it certainly wasn’t obvious to me. So ideas in foams carry over to emulsions and vice versa. Ideas that seem to apply only to making fancy microemulsions turn out to be surprisingly useful for those designing laundry detergents – a fact that very much surprised me.